Bmom's parents warning against open adoption

We were matched with a wonderful bmom a few months ago and she has been great. She has been buying gifts for us and our older children and she generally seems like a really caring, stable young woman. She has an older child who lives with her parents. I met the bmom's parents for the first time last week and had a slightly strange conversation. They basically said that I should be very careful because she can be quite manipulative. They said that their daughter regularly comes and tries to take the child back, saying she is going to parent. They said that they think an open adoption won't work and are trying to put more distance between them and her. Bmom is very close to the end of the pregnancy and I am starting to feel concerned. We were hoping for an open adoption where she would become a part of the family. If she acts the same with us as with her parents then an open adoption would be very difficult. But I don't really know if I can trust her parents or possibly she just acts differently with them because they are family etc. she has been nothing but kind towards us. I a freaking out a bit right now, I really thought this was going to be a good match and starting to feel like I don't know bmom at all :( Any advice welcome x