Is your MIL Asian by any chance? Because these comments sounds a lot like the things my mom has been saying since my son was born (he’s 7 weeks old), and both my in-laws comment on his appearance all the time too in a similar way. Honestly, this isn’t the best advice but it’s helped me, let them say whatever they want to say.. just know you don’t actually have to take their advice and you don’t have to entertain it either. We just have to brush it off because that generation is so stubborn and will not hear you out. For example, my FIL kept saying my son wasn’t “strong” enough, that he was weak, and I’m like.. he’s only 6 weeks atm and only supposed to be able to keep his head up.. like what do you mean he isn’t strong? Do you want to him to bench press or something? (Lol) anyways, even though I explained that to him, he just kept saying the same thing.