Is it obligatory for the one offering a sacrifice on behalf of himself and his household to refrain from cutting his hair and nails, both for himself and for those included in the sacrifice, or is it only for him, or is there no ritual prohibition because it is a shared sacrifice?

The gist of the Fatwa:

Whoever intends to offer a sacrifice (Udhiyah) is not permitted to remove any hair or clip any nails once the first ten days of Dhu al-Hijjah have commenced, until he has offered his sacrifice. This ruling applies specifically to the one offering the sacrifice (the head of the household) and not to those on whose behalf the sacrifice is offered. This is the preponderant opinion. The evidence for this is derived from the apparent meaning of the Hadith and the fact that the Prophet, peace and blessings be upon him, used to offer sacrifices on behalf of his household, and he did not command them to refrain from such actions.