Does this warrant any type of civil lawsuit?

If you have a realtor you're working with to buy, ask them to search for keywords like "garage apartment", "in-law suite", "guest suite" in addition to your other criteria, especially since multi-families are hard to come by in Houston.

If you pick up just one side you could file for a partition lawsuit to split your portion from the whole or try to hunt down the other party to make a deal or get them to agree to partition the whole.   

The problem I foresee for you now is, if/when you take this to court, the judge is going to be presented with two very different and conflicting pieces of evidence (an invoice for $1,500 from you and a lawsuit for $18k from you for the same property/damages) and you're going to have to explain the discrepancy

There are many investors who establish an LLC or Series LLC in one state and then place real estate from other states under those entities through the "channel" of land trusts - you would only need to pay the foreign filing fees in the case the land trust gets revoked (if there was a law suit, for example.)

If you don't have much personally now and won't in the future, you're a less appealing target to be party to a lawsuit. 

And then liability....a model just won a multimillion dollar lawsuit over bedbugs.

Find out if there are any special assessments currently levied, or if they anticipate any soon, whether or not there are any lawsuits within the association and of course whether or not they even allow short term rentals because some don't.

We currently have 2 vacation rentals on a river that will be ready for snowmobile season and a homestead on the Bay that has a two tenets in the mother in law suite.

Based on the description you gave, it's a decent lawsuit waiting to happen.But with that said, I would personally sell it at a premium.