I've seen people dividing 10 gallons in to 3 or 4 sections...but I really wouldn't divide a 10 into anything smaller than 3 sections, unless you just have some *really* tiny bettas. But, it's personal preference, I always do mine in 3 gallon minimums, with a preference for 5 gallons. But, if they've never lived in a tank that big, I'd definitely acclimate them to it first slowly, only fill it up with a couple of gallons for the first week or so, then a bit, then a bit more, just so that they can get used to swimming in all that water. And, I have *LOTS* of silk plants in mine so that they have places to rest and hide in all that new space. :)
As for the dividers, here's a link:
And for safety, I glue mine in, but many people don't, so, again, personal preference. You can use regular hot glue, or you can use aquarium sealant, either works, just make sure that it's either hot glue (which is non-toxic) or made for aquariums to ensure that nothing leeches out of it and harms your fish. :) Oh, and also for safety, I make sure that the top of my divider comes up a couple of inches above the top of my tank to make sure that no-one decides to jump it. ;)
I'm over-cautious, but I had two boys in a 10 gallon with a ready-made store-bought divider...and one day I come home and one of them has jumped or wrigged his way into the other side and the victim fish didn't make it more than a couple of days after that. I was horrified and decided to NEVER let that happen again. :( Hence the extra safeguards that are probably not needed...but I like to know that they're in place just in case. :)
Also, with hotglue, you can take the divider out if you want to later. It leaves some glue on the side of the tank, and you can either scrape that out, or you can leave it, just depends on your preference. :) So with hot glue they're not in there forever, you can take them back out again. :)
Here are pics of my divided tank and the plants in them:
Close-up of divider...and Chaucer...who is begging for yet more food...
More begging (I do feed them...), but you can see the level of silk plants in there and how they are at the surface
Geoffrey had serious ammonia burns when he came to live with us about two weeks ago, and he does not love the camera the way Chaucer does. But, here are his plants and him resting in them.
One more of plants and Geoffrey. Not sure why his eyes look so funny...they're actually blue, so perhaps something with the camera flash and the bathroom lights...or something. :)
Anyway, there's the links to the how-to and some pics of finished products. :) Good luck to you! :)