Childcare/school help!!!

So im currently a mom of two a three year old and a 9 month old. My 3 yo just started preschool this week. Within the next month I will be taking on a 2 month old to watch. I walk my 3 year old to school and usually carry my 9 month old or put her in a carrier. The school does have a flight of steps to go up but to get in and no elevator. How in the world do I get two babies and a toddler up and down lol. I cant carry both babies because mine is a squirmer and its to long of a walk from my house. What the heck do?!? Any recommendations? Im thinking mine in the carrier and 2 month old in a stroller but then how do I carrier a stroller with a baby in it up the steps while strapped to my 9 month old and make sure my 3 year old doesnt fall lol. How do I do this?!?!?! TIA!!! Any tips help!!!!