This is actually a fairly complicated question. It's difficult to say when making and selling ready-made clothing in the Anglosphere began, largely because most scholars who have investigated it have been starting from the supposition that the ready-to-wear trade originated in the mid 19th century, with feelers running back to the earlier decades in various ways.

We typically say that the first we know of ready-to-wear clothing shops relates to 17th century "slops" or "slop clothes" - produced in bulk and sold to sailors by the British navy, and sold by civilians onshore to sailors, laborers, and servants. These were cheap and loose; the navy's slops were made as uniforms, while civilian slops obviously weren't. At the same time, better clothing was also being sold by merchants, particularly pieces that needed less customization in fit, such as stockings, shoes, waistcoats, petticoats, caps, gloves, cloaks, shifts, and shirts - but also gowns and coats. For instance, a late 17th century Salem, MA merchant's probate inventory contained

a woman's yellow waistcoat; a jerkin; light-colored silk say, perpetuana, and silk barratine under-petticoats; black serge upper-petticoats and linsey-woolsey petticoats; shifts; and wool, red worsted, and thread (linen) stockings.

Many others sold stays (corsets) imported from England, and a New York merchant ordered "ready made womens Gownds of worsted & silk Crape" in 1686. Inventories from London show even more expensive goods, with one including 160 sets of matching mantua-petticoat-hood sets, and by the mid-18th century it was quite common to see advertisements in America for ready-made or London-made goods "in the latest fashion". Americans do not seem to have produced a lot of ready-made clothing outside of shoes, stockings, and leather breeches, as far as I can tell. It seems to have been typical for ready-made clothing to have been sold either by general importers (who would sell other things alongside the gowns and stockings) or by retailers specializing in one item (hats, leather breeches, etc.). For instance, John Murray and Son, at 27 Beekman St. in New York, advertised various imported cottons, cotton shirts, hats, sewing thread, salted cod, glassware, wine, watches, and hair powder in 1798.

It's difficult to tell exactly what happened in the early 19th century, because as I've said, most discussions of ready-made clothing deal in more detail with the post-Industrial Revolution world. It does seem, based on advertisements, that the sale of ready-made outerwear tapered off by the end of the 18th century and was no longer being sold, except for a) hats, shoes, stockings, chemises, etc. (pieces which worked well with some form of standardized sizing) and b) lower-end clothing. It's probable that some of this had to do with severing economic ties to Britain, and it's possible that more tailors and seamstresses had moved to America by that point, undercutting the importers. But with industrialization came a new wave of businesses selling ready-made clothing for men.

Where 18th century ready-made clothing was generally produced by people who knew their trade and either sold directly to customers or to general merchants for resale, the post-industrial system - known as the "sweating" system by the 1850s - involved less-skilled labor (in New York City, typically recent immigrants who desperately needed work) churning out garments for wholesalers who would then sell to clothing-specific retailers. In the first few decades of the century, the status of this form of ready-to-wear was on par with the secondhand clothing trade, which was not high, as I'm sure you can imagine. This gradually changed, as people became more used to the presence of ready-made clothes and as retailers aimed to bring in middle and upper-middle class consumers by providing a higher-end shopping experience. Two factors that helped out the industry at the time were that men's clothing became significantly less fitted in the 1830s and 1840s, making it easier for a retailer to deliver a non-bespoke product that pleased the customer, and that the sewing machine, which increased the amount of pieces an individual worker could make in a day, was developed around the same time and became manufactured on a larger scale in the 1840s and 1850s.

Women's clothing took longer to become a big part of the ready-made garment industry, probably because it was on the whole tighter and more closely fitted than men's clothing. Even as men's ready-made coats, waistcoats, and trousers were becoming staples in middle-class homes, ready-made dresses were seen as cheap. It's really the popularization of the unfitted shirtwaist in the 1890s that led to women's ready-to-wear becoming a huge part of the industry, and while ready-to-wear definitely did not drive the fashion industry as a whole, it's notable that less-fitted women's clothing predominated after that - blousiness was in fashion to some extent from 1900 to about 1922, when the stereotypical tubular and shapeless styles came in. That said, ready-made hats, coats/cloaks, underclothing (particularly corsets), etc. were popular and widely available in department stores from the time those began opening in the middle of the century, as well as dry goods and millinery shops.

Or did everyone expect women to sew clothes for the family?

I'm really not sure how much women were expected to sew for men prior to men's ready-made clothing taking off, apart from items like shirts that were fairly simple, but certainly sewing for themselves and other female family members and for children (particularly for babies) was common. However, you have to understand that tailors, dressmakers, and seamstresses weren't seen as artisans prior to the Industrial Revolution in the way that we use "artisan" today - they didn't cater solely to the elite and make a lot of money with their crafts. And since people didn't tend to have as much clothing per person as we do and since the fabric generally cost much more than the making, paying someone who knew what they were doing was often a decent bet. You didn't have to be a very wealthy person to have purchased bespoke clothes in the early 19th century and earlier.

Were there "brands"?

There were not really brands as we know them today for anything, as far as I know, until well into the Industrial Revolution. Garments didn't get labels until the mid-late 1860s, and at first that was just for the most high-end couture. For the most part, clothing was identified by the store that had purchased it wholesale or had it made by merchant tailors/house couturiers, rather than a brand that might be sold in many stores. Prior to the Industrial Revolution, you were either making your own clothing or having it made by/under the supervision of an individual.

It's not like there were fashion shows dictating the hot new styles...

Edited to add this sub-answer! Fashion shows have never been about dictating styles - they're about displaying new wares and getting publicity for the fashion house. Prior to fashion houses (a 19th century invention), women would get information about new styles from fashion periodicals with descriptions and plates (which started up in the late 18th century), from watching the elite women who moved fashion (aristocrats and actresses, typically), from friends closer to fashion centers by word of mouth or letter, and from their dressmakers.

Before we had machines making everything for us, would there be huge farms of people with sewing machines making clothing?

I mean, that is what we have today. All clothing is "handmade", it's just that we don't call it that unless it's made by a small business. Clothing factories in e.g. Bangladesh are full of women on sewing machines.