I bought my Lear for one 14.1 h horse. It didn't come with a divider and I never put one in. Of course, he could completely turn around in the trailer and often did!
Trailer tires aren't anything special. Just make sure they're the correct size for the vehicle and you're good to go.
I have a 1992 Adams now. NICE trailer, and the woman who owned it before me is a friend and took very good care of it. When she sold it to me several months ago, she'd just had the lights rewired and the bearings greased and repacked. The tires are in good shape, too.
The horse for whom I'd bought the Lear passed on 4 years ago, and I needed a bigger trailer for my TB. He COULD be hauled in it, but it was a tight fit and he was miserable. So JJ got a bigger trailer to fit his bigger TB self.
As long as the two horses will fit without being uncomfortable, there's no reason you can't take two at a time.