So I'm having problems on 2 macs.. my iMac and Macbook Air with SSD...
I wish I could increase the ram on my MBA, but I'm 99% sure that you can't..
I'm 100% sure you can't. I wasn't sure if it was one of the early ones that didn't come with an ssd standard. 2GB is the minimum for Lion, and many people have stated that their Airs run fine on it. I was just saying that I think they're relying on that ssd for virtual memory usage to get a smooth experience with so little ram by today's standards. Others say it's fine on older imacs than the one you own.
If I was looking into something like this, I'd look at non standard peripheral devices, programs, and addons that are used on both machines to try to determine a possible cause. If you're looking to return to Snow Leopard, you can always reinstall SL but you'd be going from scratch. You'd have to reinstall everything. You'd need a backup of all your personal files and data as well. You already suggested your computers started with Snow Leopard, so yes they'd work under that OS.
You used to have the archive and install method too, but most people did clean installations anyway due to bugs. Oh and that was for upgrades, like you could archive and install going up to a higher os version from the prior one. I can't recall if that option is even present anymore.