Ungh, copyright and residuals and legalities. This is SO not my area of expertise, though it does have a lot to do with music. I'll weigh in where I can, and do some more research to see if I can come back with more.

First off, most composers then, as now, worked on a commission basis. That is, someone with money would ask for a sonata/concerto/opera/mass/whatever of X instrumentation for Y length, and they would work out a deadline, and payment, and all that jazz. Now, while the commission was by Baron Lotsofmoney, it's not like the Baron could just go out and sell the copies to anyone, or sell the rights. Often composers would print their own works and sell them, but copyright laws were... fucky.

I'll send you off to a cool legal case: Bach vs. Longman. Several of the (ludicrously numerous) sons of the famous J.S. Bach went on to become composers in their own right. One of them, Johann Christian Bach found out that copies of his works were being printed and sold in England, and decided to sue. He claimed that his works were copyright to him, and the English printers said that music didn't count as printed material, but Bach won, and gained rights to his printed works.

http://www.copyrighthistory.org/cam/commentary/uk_1777/uk_1777_com_1072007112559.html http://www.tandfonline.com/doi/abs/10.1080/02690403.1995.11828226?journalCode=rrma20

So, yes, composers could print and sell copies of their works. Handel did this extensively, but didn't really copyright his work, he just printed it himself in huge quantities for very cheap (side note, Handel was a total whore and would totally rewrite his music for whoever wanted to perform it. Want to do Messiah but don't have a good tenor? Let me rewite all this stuff for soprano, hence the many varied versions of Messiah, which is never performed in entirety).

As for whether Beethoven paid Schiller, since Schiller died decades before the premiere of the 9th Symphony, it seems pretty unlikely. Now, whether or not copyright in the 18th and 19th centuries extended post mortem, or to the estate, I have no idea. I know Constanze Mozart made a lot of money off of Mozart's compositions, but she had them published herself after his death, so likely she would have owned the copyright. I know the Statute of Anne - the UK copyright law that J.C. Bach was challenging had an expiration term of 14 years, but I don't know if it would end automatically on the death of the copyright holder, or pass on to the estate. I also don't know the copyright laws of all other relevant European nations at this time.

Which brings up another point, is cross-jurisdictional copyright. If you're a German composer (Beethoven) living in Austria, who wants to publish music in France, how does that work? Europe, then, as now, has many rules governing many regions and those would have to be navigated (and challenged) by composers who want to publish their works, and ensure they're not published against their wishes, or without compensation.