How to get two toddlers napping?!

I’ve got two one year olds (on 15 month and one 18 month, the 15 month is my nephew in my care) and I’m having such a hard time establishing any kind of reliable routine. Some days they go down for two naps and sleep about an hour each and some days i can’t get them to sleep at all. The 15 month old one always seems to wake up the 18 month old one. The 18 month old will go to sleep on her own in her crib but my nephew won’t, I have to rock him and then sneak him down without waking him. Anyone been in a situation like this maybe a twin mom who has been through some stuff wants to pass on some secrets? I’m starting to lose my mind about this, worrying like crazy. And of course, my house is a mess and nothings for dinner.