You can't do it, at least not without some highly complex and mega-expensive equipment.
Your only practical solution is to convert all the sources to DC, then combine them before using a single inverter to produce AC out again.
Even if you took the one source you can't adjust, the line AC, it would be impossible to synchronize a generator to it. The generator speed will vary under load so keeping the exact frequency and phase is not achievable. The PV inverter isn't difficult to sync to the line AC but it too would be impossible to sync to the generator.
Brian.