Rams for 10g

Many here will tell you a 10 is too small. I think a 10 gal is risky. I've found that it depends a LOT on the specific fish you get. (What conditions they were raised in/where they're from, etc.)

I've found that rams are very active fish with great personalities. It's possible to keep a single ram, but after seeing my pair interact, I wouldn't have the heart to keep one ram by himself.

In my opinion, you'd definitely want to take the molly out, especially if you try a pair. My rams know that they're the king & queen of the tank, and they keep the swordtails out of their space. In a 10 gal, I don't think there'd be enough room for them to establish separate territories. The 3 cories might even be an issue. If you're really set on rams and the 10 gal, I'd move the cories as well. You could replace them with a few ghost shrimp, maybe.

Rams prefer acidic water. However, my pH stays at 7.8 and my rams are quite happy. As many often say on this board, a stable pH is better than an artificially changed one.

I'd also suggest that you do a search on this forum for "rams" or "german rams" and scan through all the information you can find. There are a lot of good suggestions buried in those hundreds of search results. One especially important thing is to acclimate them slowly. I floated their bags in my tank for several hours, adding a little bit of tank water every now and then. This is especially important if your pH and other parameters differ from the LFS. Be sure to ask about the LFS's pH, hardness, temperature, and other water conditions.

I'm not sure if this is what you want to hear, but a pair of rams would be much happier (and easier to care for) in your 29. I know nothing about rainbows, so it's possible there'd be a compatibility issue there, but it's worth thinking about.

I am currently having good luck with a pair of rams in a 10g tank. I do think, however, that this specifically depends on the fish that you buy. It could end up in mating or it could end up in disaster.