There's a lot of chat about mixing generators in sync - I've tried a few different brands and sizes. They all work. It's basically just sensing the 50/60hz and doing it's own sine wave timed with that. The more complicated thing with generators is balancing load as the motor side needs to be adjusted with load. This is done by voltage sensing and this is where the brands can differentiate. i.e. one that senses a need for more input at a lower voltage is going to take the lions share of the load. I suspect this might be less of an issue when the supply side is 12/24V batteries. Would a 2000W and 300W give you capacity of 2300W? Unlikely but two same brand 1500W might be close to 3000W.
[Honda generators run a little higher voltage so take a higher unbalanced load when paired with other brands - then total capacity is limited by when the first generator trips, followed immediately by the other side when it suddenly bears the full load itself]