We all are in the same boat mummy.
What works for us is
a) both of us are in the same team - so as a couple, we set some ground rules about naps, screen time, and meals. No one is allowed to break them unless we are on holidays.
b) We let the grandparents have their way about other things, like taking the kids to the park, dressing them up, brushing the teeth. That way, the grandparents feel involved without disturbing the important routine.
You have to understand, it is difficult for anyone to choose between mum and partner. So, best avoid such situations. Explain to your husband how important routines are for a baby, how your 1.5 yo should have zero screen time.
At the same time, try your best to be amicable to your mil. So, when your hubby talks to his mum, he can say," listen to her, she is nice to you, isn't she?"
hope this helps.