hard to say... the 2.5 gallon can't be any fun for the frog.
I personally believe that the 12x12x18 is too small for even one white's. The 18x18x24 would comfortably accommodate 2 white's. Also, even though they were once roommates, you would still want to quarantine the new frog for at least 30days, so either way you will need to get another enclosure.
I would strongly suggest getting a larger enclosure before adopting another frog... You could use the big tank for the new frog and then after 30 days move Azy in with him.
Or, maybe someone else will adopt the remaining frog soon?