Is it permissible to accept the invitation of the husband's irreligious family to their holiday celebration, and to accept gifts from them, while suggesting giving gifts to children on Islamic holidays to avoid family problems?

It is not permissible to congratulate disbelievers on their holidays or to accept their invitations to celebrate them, for that entails an affirmation of their falsehood and participation in it. Treating them well does not justify attending their holidays, because matters of religion and creed do not tolerate compromise. Allah suffices those who fear Him and rely on Him from problems. Patience in upholding the tenets of faith is among the greatest acts of devotion to Allah. As for gifts from them on their holiday, there is no harm in accepting them; rather, it is encouraged if it softens their hearts towards entering the religion, and the holiday has no bearing on preventing the acceptance of their gift.