It actually popped up in another life state dynasty I read;
and per the rule, "the first life state that is different than the heir and not already used as an heir is the new heir." is the gist of it, so you have to deal with a human heir until young adult and all requirements are done I believe it is....(Check the rules thread to be sure) before you can change a heir's life state.
You can't change the life state of an heir at all. No Ambrosia, no biting, no nothing. Please,
please check things on the rules thread before saying this! You are
potentially jeopardizing people's dynasties and this is not the first time. If something like this comes up and you can't find the ruling, it is far better to have the question asked again in the rules thread than to have someone fail a dynasty because you gave them misinformation. I do not want to see anyone fail a dynasty because they are told something that is incorrect when it's there on the rules thread and Metro and Rica check questions there once a day.
Snuffles, just to clarify, you have to choose either Peeta or Finnick as your heir. They come from the first birth to have a different lifestate to all of your others so far, and it's not a requirement that the lifestate is the same as the heir's spouse. You are also not permitted to change either of their lifestates. At least you've gotten your human out of the way early.