Lemon balm is not a mint so it can't cross with any Mentha species. The mints might. You'd just have to evaluate any seedlings for scent and flavour to see if they are worth keeping. But the main problem will be runners, not seedlings.

Named mint varieties are propagated by cuttings or runners to ensure the flavor ... any seedlings might be decent or inedible.

Not sure why you would be letting them set seed to begin with. If you want to allow them to flower for pollinators then fine but you should be clipping the spent flowers as soon as they start to fade.

Rodney