What is the ruling on the prayer of the Imam and the congregants if the Imam had eaten camel meat without knowing it, and then led the prayer, and is the mother sinful for not informing him?

Eating camel meat is, according to the preponderant opinion, one of the things that nullify Wudu (ablution), and this is the madhhab (definition) of Imam Ahmad. The prayer of one who ate camel meat is invalid if he prayed without Wudu, and he must make up for it. As for the prayer of the congregants (ma'mumeen), it is valid and is not affected by the invalidity of the Imam's prayer. The mother should have informed her relative, because that falls under the category of obligatory advice, and Allah has forgiven her forgetfulness. She must inform him after remembering so that he can rectify the situation. All of this applies if the man adheres to the opinion that Wudu is nullified by eating camel meat; otherwise, his prayer is valid.