Actually, hamsters are usually better off separate. They're solitary animals and if you have two that grew up together, take them apart for a while and then put them back together, they forget they knew each other and will fight. I hope your bigger set up for them helps.

Lucky you didn't get the hamsters I had to deal with when I worked in a pet shop. I called them vampire hamsters. Really nice looking, but nasty and terrified. Their first instinct was to bite and bite hard. I always had band aids and lost a bunch of blood to those guys. A family with kids wanted to buy one, but I wouldn't let them.