. Now tonight I read that your confirmation sponsor must be validly married. My MIL was/is in an invalid marriage.
Well no. That is not accurate. The actual canon law requirements for baptism and confirmation sponsor are as follows;
*Can. 872 Insofar as possible, a person to be baptized is to be given a sponsor who assists an adult in Christian initiation or together with the parents presents an infant for baptism. A sponsor also helps the baptized person to lead a Christian life in keeping with baptism and to fulfill faithfully the obligations inherent in it.
Can. 873 There is to be only one male sponsor or one female sponsor or one of each.
Can. 874 §1. To be permitted to take on the function of sponsor a person must:
1/ be designated by the one to be baptized, by the parents or the person who takes their place, or in their absence by the pastor or minister and have the aptitude and intention of fulfilling this function;
2/ have completed the sixteenth year of age, unless the diocesan bishop has established another age, or the pastor or minister has granted an exception for a just cause;
3/ be a Catholic who has been confirmed and has already received the most holy sacrament of the Eucharist and who leads a life of faith in keeping with the function to be taken on;
4/ not be bound by any canonical penalty legitimately imposed or declared;
5/ not be the father or mother of the one to be baptized.
§2. A baptized person who belongs to a non-Catholic ecclesial community is not to participate except together with a Catholic sponsor and then only as a witness of the baptism.*
At this time they are living as brother and sister–I have no idea if this was true at the time I was confirmed.
Nor is it any of your business. You should, in charity, presume your MIL is a Catholic in good standing and under the guidance of her pastor.
.Does this mean that my baptism and confirmation were invalid?
Why do you think the validity of your baptism or confirmation is dependent on your sponsor?
.Surely not, but it’s still upsetting.
I’m not sure why.
.My husband–a baptized Catholic-- was also present
But not your sponsor.
.although your confirmation sponsor must be of the same sex
Not true.
.A female Christian friend was also present, but, again, I know the sponsor must be a Catholic.
Correct, a non-Catholic is not a baptismal or confirmation sponsor.
. Is this silly to worry about this?
I am not sure why you would be worried.