The first tank would be the bare minimum.....the standard is 6 square ft of floor space for the first adult and 2 square ft of floor space for each additional...those are the minimums....
Personally, if I were you, I'd get the first tank and put the 2 females in it and then get a slightly smaller one and house your male in it.....
I have many dragons and have many adult males over the years....I've only had one I could house with females full time...they are usually relentless breeders and stress the females.....so for optimum health and happiness for all concerned that's what I would do....just my opinion.
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Tracey 
Tracey's Beardies
www.beardiecrazy.com
"Whining is not only graceless, but can be dangerous.
It can alert a brute that a victim is in the neighborhood" ~Maya Angelou