I believe 75g is the general concensus for an adult. I'm not sure for two, but I know you'll get a lot of discouragement against it due to fighting an/or constant breeding stressing out the female.
The only person I know with two beardies together raised them together and got lucky in that they were both females. They are quite happy together, but the impression I get from this board is that's not the norm.
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1.0.0 Thoroughbred
0.0.1 Mali Uromastyx
0.0.1 Bearded Dragon
0.0.1 Corn Snake
0.0.1 Milk Snake
1.2.0 German Shepherds
0.2.0 Cats
0.1.1 Birds (Conure and Cockatiel)
1.1.0 Rabbits
4 Fish tanks (SW and FW)