You could take them on a special trip for a weekend to Disney or Sea World or even Galveston to the beach (an expensive idea, granted, but they are just the right age for something like that). Or, you mentioned game night...do they have any board games? Everything doesn't need to be electronic. You could get them some fun board games that they could play together and that you could all play as a family. I think some of the easier ones (Candy Land, Chutes and Ladders, Hungry Hippo, Operation, Guess Who) are geared towards kids that age.
One other thought...do they have bicycles? I know most kids do, but that is another idea if you live somewhere where they can ride them. You and your husband could get bikes too and go for rides as a family. I think Target and WalMart sell inexpensive bikes if you aren't looking to spend a ton.
There also is a place called Sweet and Sassy that does little parties for girls (there is one in Sugar Land...not sure where you live, but it's a chain). They can get little makeovers (nails, makeup, etc.) and they have a little runway that they can do a fashion show or something. It looked cute. My daughter is only 18 months old. We went there for her first haircut, but they had packages for older girls. Could be fun for them!
I hope some of these ideas help. I know it's really hard when you just don't think you need anymore "stuff" in your house. Good luck and have fun!