Yep something like a 50G (us) and they should be fine.
You might want to consider dropping one (or two) groups of tetras to increase the size of the other groups.
Something like the below would be my choice:
15 Cardinal tetras
15 Bleeding heart tetras
15 Green Neon tetras
Thats just my personal choice though as with tetras I like having just a couple of large groups of one or two species in a tank.
I love tetras so make sure you take some photos and put them up somewhere on here. What size of tank are you planning and how are you going to set it up/decorate it?