Grandfather can’t legally come to my wedding (NEED ADVICE)

So I’m American but I now live in Japan and am engaged to my boyfriend who grew up here. We decided on just a tiny wedding with only super close friends and family since we know extensive travel for large groups would be super hard. After hELLA back and forth we decided to have the wedding in Japan since he had a few more guests than I did and while I have Japanese citizenship he can only go to America as a tourist. Idk legally and financially it was just easier.

The only thing I didn’t consider is that my grandfather cant legally leave the US at all because he has a felony due to too many DUIs (drunk driving, he was an alcoholic for 20 years but has now recovered). I’ve searched online but can’t seem to find or understand much. Is there any way we can get some kind of court order to let him travel?? Alternatively we also found that Japan might not let him in due to this as well. Honestly it feels like everything is crashing down. He needs to be there, we’re super close and he’s pretty much a father to me so him staying behind isn’t really optional. If anyone has any advice, tips, or experience it would be greatly appreciated!!