Mother in law hindering potty training

Angela • FTM to identical twin boys 💙💙

I know I’m just the “step-mom” SO & I aren’t married yet. We’re expecting identical twin boys by April, and so we’re trying to potty train his 2.5 year old boy... But man does my SO’s mom annoy me & push my buttons.

I don’t do anything with his kids without discussing with my SO first, so everything I’m doing with HIS kids (5 year old girl and 2.5 year old boy) is because it’s what my SO wants and I respect it.

He’s had a few accidents here & there, as to be expected when first potty training, but he’s peeing AND POOPING on the toilet for us now 😭💙 he used to HATE pooping on the toilet. And has been REALLY good for the passed 3 days in a row. Well, we had a babysitter today, (we live with my SO’s mom until we save enough for deposits which will only be about another week or so until we have our new bigger place on lock) and he had an accident. And my SO’s mom told the babysitter to just put him in a diaper because he’s “obviously” not ready. She is the only one not helping with potty training. She sees it more as a chore. And is only hindering his process as we only put diapers back on him for nap and bedtime for now, until he’s better with no accidents during the day at all.

So I get a text from the babysitter that she was told to put him back into a diaper by my SO’s mom. Which my SO and I don’t agree with. And she’s not the one who pays the babysitter either.

But I guess his mom wouldn’t leave the house again until after she saw him put a diaper back on the 2.5 year old (he’ll be 3 In July and we’re trying to get him potty trained before the twins get here by April but she’s making it very difficult)

How would you approach her? She doesn’t like confrontation, and always thinks everything is an attack on her.