I took in a young girl and her kids and now her husband will not let us see them: Advice?

I have never posted on here, but I do read a lot of the posts. I need some advice. Seven years ago, we took a girl and her baby in. While living with us, she has another baby. The kids are 7 and 5 now. They both have lived with us their whole life. Their biological grandparents on both sides have never had anything to do with them. They call us Nana and Papa. Well, a couple of months ago, she meets this guy online and starts dating him. She only really saw him like three times. Well the beginning of November, they sneak off to the courthouse and get married. They really don’t know each other, and the kids don’t even really know him. She is an adult, and I know this. He is very controlling and doesn’t let the kids do anything. He doesn’t want us to know where they live, which is whatever. My problem is that he has put a stop to me seeing and talking to the kids. It is killing me inside. I think and love the kids as if they were my biological grandkids. My question is, would you just let it go and try not to see them or do whatever you can to see them? They stayed talking to us up until the day after Christmas and then haven’t heard anything from her. He wrote to me and said that he wants nothing to do with us because we asked her if we could keep the kids over the weekend, and he doesn’t want them to. Sorry, this is so long. Please give me advice on what to do. Please post anonymously.