itch.io

before hatching the eggs, keep going to nests and find the mon that you want, then when you have enough, hatch them

so there are 2 ways

1: In the village you can build the nest.  it will cause a monster to always appear in the starting selection,  this can cause 2 to appear at the same time.

2: more complicated method, the option called egg sense lets you get specific monster eggs, but it won't offer ones that are already in your party.  it doesn't care about your inventory tho so as long as you don't hatch the eggs, you can stack up multiple of the same. when you have as many as you want hatch them all at the same time