I personally think that your terrarium would be to small for 3 barely adequate for 2. I have been told numerous times on here to try and go by this simple rule.

1 frog per 10 gallons. Now greys are smaller so 2 might be ok but not recommended... but definately too small for 3.

But I must agree the way you decorate and set up your frogs home is a huge factor... perches, branches, hideing spots, all help.