C.K.
I dont want to be harsh, but the only help it seems necessary to give here is to remind you what it was like when you had your first child, and random family members were telling you that the decisions you made for your children were wrong. or snickering behind your back because they thought you were making ridiculous decisions. This isn't really your "problem" to be asking for help on, nor does it seem that you've been asked for advise or your opinion on the matter. It seems you just want to be "right". The best advise one can give you is to back off the couple. It's their decision. If they ask for advise, give it, other than that just support them. Thats all they really need right now. Love and support. Not opinions or judgements.
Also for the record, I believe in a Methodist church this is fine. The position of the church is not necessarily that the godparents take the kids if something happens, but gives these people spiritual responsibility for the child through their religious path.