I have a Sister In Law like BM. When i was carrying both my Girls (now 8&4) she was pregnant at the same time. My girls are 8 & 10 weeks older than her Boys yet she announced both pregnancies before i did. She was gloating that she was providing the first grandchild in my Husbands family & was very put out when this wasn't the case ! She even said on my second pregnancy that i 'stole her thunder' (she told everyone at 6 weeks & i waited until 20 as i had a few complications & wanted to make sure everything was 100000% safe before i told the world). When i started weaning, so did she, same with potty training. She always wanted to 'compete' which is utterly ridiculous given the age differences & i felt like she never enjoyed the stage her Babies were at, she was always racing ahead to the next milestone. And trying to 'one up' my daughters with her Boys achievements which baffled me.
I sneaked in a lockdown Baby last year & despite the madness of a pandemic, it was so lovely to be able to be able to enjoy my pregnancy & new born Son in our bubble without her telling me that her 6 week old was walking to the kitchen & making his own breakfast or whatever bull she came out with ! This is how Georgie come across with her 'My Kids eat Olives & feed their own bottles' etc