While there will be voltage at both terminals, the inverters will choose only one source (in your case phase) to connect and synchronise to.
It should be ok as long as you don’t have any wiring mix ups. In theory when phse on ac 1 has a blackout it could switch to the other phase if it was still live
AC 2 out shouldn’t overload the phase if the inout current is set correctly.
Have you worked through the three phase parrallel training and manuals?