Family accounts only became a thing in March/April 2022, so it's quite likely that for many people the full 2 years has not yet passed for any miles transferred to the head, or that any miles transferred more than 2 years ago have already been consumed.

In short - there are probably not many Family Accounts where the head has status and miles that were transferred from a family member over 2 years ago would still be untouched in the head's account.

However, if the family head has status, then it would most likely be the case that the miles don't expire.

Unless and until someone in that very specific circumstance shows up to clarify the point in an authoritative way, we collectively can't say for certain.