I have 2 wonderful grandchildren whose other grandfather is Jewish. However he isn’t an observant Jewish person, nand nor are his kids (my daughter in law is Christian, my son is Christian Catholic). That said, I think it’s important for my grandchildren to learn about thisother part of their “family tree” and my son and daughter in law have said I am welcome to teach them about it since I find it so important. Now, I grew up in nyc and had friends from every faith tradition when I was younger, but I now live in Ohio and unfortunately my social circle is small and I don’t know any Jewish people here, so I don’t know where to start. Can you share the name of a synagogue that would be open to a non Jewish person attending and learning about the Jewish faith with my grandchildren? Thank you.
So from the way I understand your question, your daughter-in-law's father is Jewish. Right? Well, sadly, if your daughter-in-law's mother isn't Jewish, that mean she isn't either, which means your grandchildren are one hundred percent not Jewish. (This isn't a bad thing, necessarily, although it is sad that the Jewish grandfather chose to intermarry, which is a sin according to the Torah.)
Therefore, any education you want to give your children on Judaism should not be done with the intention of showing them at they are Jewish, because they aren't.
Taking your grandchildren to a Jewish establishment to help them learn about Judaism might give them the wrong impression that they are Jewish, and it might come as a shock (or disappointment) when they learn that they aren't considered Jewish at all.
I'd suggest finding a video or something, or teaching them what you know about Judaism yourself. They don't need to learn the ins and outs of the religion, because they aren't Jewish. You mentioned that you are Catholic, therefore you should be familiar with the story of Abraham, the Exodus, etc.