Is offering a fidyah (expiation) of a sheep sufficient, or is a camel required, and is redoing the Umrah obligatory, concerning what happened when the questioner's nephew's back touched a boy's, leading to the emission of semen while in a state of ihram?

You have committed a great sin by mistreating your relatives and doing so in the sacred precinct of Allah. You must first repent.

Regarding your Umrah, since you are unsure whether you purified yourself from the major ritual impurity (hadath al-akbar) before performing it, your Umrah is invalid according to the majority of scholars, because purity is a condition for the validity of circumambulation (Tawaf).

According to the majority opinion, you are still in a state of Ihram (ritual consecration), and you must go to Makkah to complete your Umrah (valid Tawaf and Sa'y). If you cannot reach Makkah, then your ruling is that of one who is prevented (muhsar), and you must offer a sacrificial animal (hady).

What you did regarding the prohibitions out of ignorance does not incur any penalty, but as a precautionary measure, if the prohibitions involved destruction (such as cutting hair and nails), you must pay a compensatory offering (fidyah) with the option to choose: fasting three days, or feeding six poor people, or sacrificing a sheep.

You are also required to pay a compensatory offering for the emission of fluid and direct physical contact that occurred. If you have already offered a sheep, we hope that it is sufficient.

You are still obliged to complete your Umrah, or offer a sacrificial animal if you are prevented, and if you cannot, then you must fast for ten days.