Is it sinful to doubt the validity of one's confirmation?

[stormyweather]

My sister, her husband, and children are getting confirmed in an Society of St. Pius X chapel. The problem, besides the fact that the SSPX is in schism, is that both adults have already been confirmed. She was confirmed in the late-60s and he was confirmed in the early-90s.

Is there sin if, through lack of faith, you doubt that the Church’s sacraments or rites “worked” and so attempted to repeat them?

 

[Michelle_Arnold]

Although deliberately attempting to repeat an unrepeatable sacrament such as confirmation is objectively grave matter, mortal sin requires, in addition to grave matter, full knowledge and full and free consent of the will in order to be committed (cf. CCC 1857). If all three conditions are not present, there is not a mortal sin. Presumably, your sister and her husband are not deliberately choosing to attempt to repeat a sacrament that they know they have already received validly; presumably, they believe that the sacrament they received was invalid. Assuming that their confirmations were offered validly, they are objectively incorrect but, we may hope, not personally culpable of mortal sin.