I am not a theologian but I think that if a person “merely” says he no longer believes, he is not excommunicated, i.e. has not formally left the Church. (I did hear that a person who had an abortion had to first go to a bishop to receive the sacraments, but I have no reference to back that up.) There is also the situation where a person may sign a docuмent where they reject the Baptismal vows (Raelians promote this), but sounds that your relatives have “gone the way of the world” and need some big shock to wake them up.
I guess that is God’s work, and we must beg Him for that possibility.
You probably have more chance to bring back those who say they are confused. Just find out their main points of confusion and have literature to help their confusion.
I wish I could get so close to my family members!
As for what steps one would need to take, they should approach a priest and ask for the Sacrament of Penance. The priest should take it from there.