You can get an advance for non-exclusive, that is correct, but a much bigger one for working exclusively.
Well, library owners can behave like little tin gods at times. Some are cool with you placing tracks elsewhere, but more than you think absolutely hate to see you doing well elsewhere as well. It all comes down to human insecurities. Seriously, I have seen the most childish behaviour at times, it boggles the mind.
You said your main thing is family/adventure. That style will always be in demand, however there is little demand for it, in that a lot of trailer libraries don't even bother with that style, and the ones that do, have an album or two, and then they've got what they need. It's very similar to jazz albums with non-trailer libraries, once they've got a few good albums under their belt, they don't need more.
So with that in mind you would need to work for other libraries, if that's the only trailer style you'll be doing. If you are going to cross over to other trailer styles, the
Piano Piiiiiiing, Braaaam, Hit, Sutttt-t-t-ter rrriiiSSSEEE HIT etc style, Bish Bash Bosh, is harder to get right production-wise than you might think, even if it is undoubtedly musically obtuse most of the time.
Not sure any of what I have written helps, but life is never cut-and-dried, is it?