Am I too sensitive?

My Son is the first grandchild for both of my parents and my husband’s. And he is going through a phase that he would not go to any other people but me. And also terrible two phase.

Last night we went out to dinner with my husband’s parents. My son usually doesn’t sit still in his high chair unless I put YouTube on for him. That way, we can enjoy our food. And last he wasn’t having it. He would not sit still, wanted to walk around and stuff. And when his grandparents wanted to hold him he refuses and hates it. And my MIL goes “you better behave better because your competition is coming. “ because my SIL is pregnant and due in September. It didn’t hit me until this morning. And now I think about it, it was kind of mean. So when the baby comes, she would love my son less ? Just because he is going through a phase ? I truly believe he will grow out it and they called me this morning to tell me they are concerned about his behavior? He is only 20months old. What do they expect from him ? Am I being too sensitive?