If you aren’t practicing, what are you walking on eggshells about? Would you rather your grand kids go to mass every week with a full spiritual life or go to Temple twice a year?
We believe in the same God. It’s not like I’m asking her to deny her belief in God.
They have chosen to remain Jewish although they are not practicing Judaism. If you ask them about it, they will tell you that it doesn’t feel right for them to give up their “faith”. I understand your question but in 57 years on this earth have never met a Jew, whether a believer or not, who felt pleased that is child or grandchild was becoming active in another church.
Even if they are culturally Jewish (bagels and Seinfeld?) they remember the scene in Fiddler on the Roof when Tevye’s daughter married a Christian and he went into mourning. I am almost sure that they won’t do that themselves, but I am equally sure that they will think of that scene and relate to it.