Welcome to the forum! It is indeed difficult to figure out what you are asking. For one thing, what do you mean by trails? If you mean paved or otherwise improved bike paths, you don't need a mountain bike. A fatter-tire road bike is fine for that, and certainly a hybrid would work.

Really, local knowledge is a good thing. There are truly excellent bike shops in San Antonio. Ask the guys that work there. They know the area. Don't expect a department store's employees to know what they are talking about.

FWIW, I find a road bike with a more relaxed frame geometry and fat tires, to suit me, on everything from pavement to dirt paths, but I ride flatter terrain than SATX.