Waalykum salam brother
Thank you for your Question
You have all right to be concerned since your wife and her brother in law are na Mahram and any such interaction should be avoided.
However, I’d suggest you get some counseling for yourself at this point. When a woman praises another relation, she is trying to hint that there is something missing in their own and that the husband should roll up his sleeves and try harder.
While comparing self to others is wrong, but if you feel that she maybe wanting and expecting something else from you, then make sure you complete remove this between yourselves by having a good communication bridge. Once you’re able to speak to one another without the fear of the other getting angry or judging, you will be able to have a more compatible life.
This is even more important because you’re going to be parents soon InshaAllah.
Hope all goes well and you’re able to enjoy your child together