The last picture isn't a grenadier, but a pioneer.

Anyhow, the uniforms and equipment are a mishmash of random pieces. Picture #6 shows a soldier with both a musket and a sword. Swords were strictly for officers, possession of a sword by the rankers was illegal. Officers did not wield long arms so, if he is indeed an officer, he shouldn't be holding a musket. Also, all on duty officers wore a gorget, which was a small rounded metal piece worn around the neck like a large medallion. Furthermore, officers wore a red sash as indication of their authority, so with #6 missing all these pieces it just doesn't make sense.

Add on question!

In Revolutionary War 'mythology', a lot of the times Americans were depicted as a sort of "rag tag" group of fighters who didn't wear uniforms while the British were depicted as always wearing nice, well-kept red uniforms.

Are these depictions generally accurate?

Let me see if I can add some in-depth critiques here:

Problems throughout: Inexplicably, all of the British soldiers in the game are carrying what appear to be stylized versions of French muskets. The British Short Land Pattern Musket was held together by small pins, and generally had brass fixtures. The muskets in AC3 have steel barrel bands, like the French muskets of the period.

The cut of the facings - the different-colored trim of the uniforms - is pretty wonky (except for image #2). The cuffs look more more late 17th/early 18th century than what was worn at during the revolution.

Specific comments:

In image #1, the British soldiers are waving the modern flag of the United Kingdom, not the flag of Great Britain. Note the lack of the Cross of St. Patrick.

Image #2 shows fairly generic British soldiers, as red coats with blue facings was the standard uniform of Royal infantry regiments. However, only a few units of the British army were expressly "Royal" - others wore the colors of certain regions or lesser nobility. I believe this cutscene was at the Battle of Bunker Hill? If so, these soldiers must be from the 5th Regiment of Foot, the only regiment at that battle wearing blue facings.

The soldiers in image #3 are carrying their muskets at port-arms, a position that I don't think existed in 18th century drill manuals. Also, I think that guy in the middle has a chinstrap beard. Facial hair of all types was deeply unfashionable in the English-speaking world at the time, and strictly against military regulations.

The soldier getting stabbed in image #4 is wearing green facings, which none of the units garrisoning Boston wore. Also, being that his unit is in garrison, he would not have gotten away with wearing a round hat instead of the regulation cocked hat.

The soldier in image #5 might be from the 14th Regiment of Foot. As an officer, he should really be wearing some manner of metal epaulette on the shoulder.

In image #6, the man appears to have a sword-like bayonet on his musket, rather than the usual thrusting/stabbing triangular blade used during the period.

I believe one of the men in image #7 is supposed to be General Braddock, famous for exemplifying British attitudes of military pomp and stuffiness. Why he is wearing an unadorned and cheap-looking private's coat is totally beyond me.

As /u/pllew mentioned, that last image is more of a pioneer than a grenadier. Pioneers were something like combat engineers, tasked with cutting their way through the abatis and other obstacles around enemy positions. I don't know why he is wearing a white bearskin cap.