I mean if I connect 2 of them in parallel, will I fry them or will they work together?
If you mean connect the AC inverter outputs together then no you can not connect any of the inverter ac outputs together.
Some people on this forum have connected another battery to the DC input port to gain more capacity. It would need to be at least two 12V batteries in series, or a combination that yielded between 16V and 60V.
No, you cannot connect the output of 2 AC inverter to get 2x the power unless it is specifically designed for that with feedback control. The wave will not be in phase and will destroy itself.
You also cannot easily connect two DC output in parallel and get 2x the power (unless specifically designed). This is because their output voltage won’t be exactly matched and the one will be supplying more of the current. In practice, this sometimes can be done if they are close enough as the resistance in the wire may equalize the voltage, but is not recommended. Maybe you can do 1.5x rated power but not 2x.