Peter is fine because if in the end everything goes to shit and he loses his fiance you know he will take up the offer that Lisa gave him but after the post-heart break phase.
The mom didn't need to come into the picture all she did was introduce everyone who the brother is dating that's it and the confession was already going to happy and just made us wait longer. (p.s. I realized the waifus quality depends on the size of their breast the smaller they are the better...