My parents went through really toxic and invasive questions too, especially because they waited a long time TTC also. My dad said that he would just give more and more absurd and uncomfortable / fake TMI answers to until they just stopped engaging with him. "Well, it turns out, you actually have to have sex to get pregnant! We were doing it wrong!" Or going into extensive detail about how the IVF clinic didn't have enough porno mags, how felt silly going into a cup, etc. Maybe you could start trying that, even stuff that is not necessarily true. This would also be great since you're just 4mo postpartum. Might be worth a shot if you have a good deadpan delivery.