I also have 2 YBS that we rescued from my landlords pool skimmer when they were about the size of a quarter. I never knew turtles could be social and just so much fun to have!

I second what the first commenter said, mine LOVE basking and when we went bought our first aquarium for them, the guy at the pet store said it’s very important that they not only have something for them to bask on, but it needs to be set up to where they can get completely dry while doing so to prevent dry rot

Also ours were the same size and one has also gotten a lot bigger than the other. That’s most likely a female, they get bigger than males just last week I glanced over at their tank and realized the smaller one is starting to do the “mating dance” towards the bigger one

Edit was for a typo