Allhers is right. Have your son talk to the local priest. Most churches have baptismal prep classes for both the parents (even the non-Catholic one) as well as the godparents.
Their marital status may be questioned as well as their intention to raise the child Catholic. However, the baby is not prevented from being baptized even if the parents have not received all their sacraments or are in a sacramental marriage. The ideal would be for them to normalize their own relationship with the church, as they get their baby baptized.
Tell them in selecting godparents, 1st of all, they must be Catholic , at least 16 ys.of age and confirmed in the faith and hopefully practicing their faith. Not because they represent the parents, but they represent and witness the church to the little one. Perhaps this little one will be evangelizing to his/her parents and they will pursue further into the Catholic church and become fully formed in the faith. God works in many ways, why not through your little grandchild?
There is a wonderful website for lapsed Catholics or for people who want to learn about our faith. Check it out. http://www.catholicscomehome.org/