They should fare okay with tankmates, with some caveats - make sure that their tankmates can't be mistaken for another male betta (i.e. long fin on sailfin mollies, bright colors, etc.) or else he'll go after them. The second caveat, but I don't know if this will apply to you, if there's more active/aggressive fish in the tank, go with a shorter finned betta, likewise if you have strong currents.