@daisy83 This sounds a lot like our situation with night wakings (4 month old, 2 year old, and 4 year old) except my 2 year old is still nursing too.
I handle all the night wakings with nursing (the baby and 2 year old) and my husband handles the 4 year old when he wakes up which is once a night or occasionally twice.
I will say if my 2 year old wasn’t nursing my husband would sure as heck be handling her night wakings since I’m nursing the baby every couple hours.
We take the approach that while my husband is at work, my job is being a SAHM. When my husband is done with his workday, we split the house/kid load and that definitely includes nighttime parenting for us.
Nights look like this: we co sleep, so basically my 2 year old and 4 year old start in their own beds, and baby is in bed next to me to start the night. So baby, me, husband is the order across the bed; I’m cuddle curled around baby. When my 2 year old wakes up, she comes into our room in between my husband and I so I can flip over and nurse her as she wakes and then cuddle curl back around baby. When my 4 year old wakes up my husband either goes and lays in his bed with him or he lays on the other side of my husband on the edge of the bed. So neither of the big kids are next to baby but we still manage to co sleep with multiple; it’s what works best for our family.
Good luck and I hope you can find a way to get some decent sleep!!