I have 2 DC's. a 3 year old DD & a DS 7 months. My DD slept 12-13 hours straight. My DS is an awful sleeper 
I share DD with her dad half the week, so at times she isn't here for 4 nights, then 3 etc.
During these times I have tried to install a good routine with DS & he is now sleeping for longer periods (sometimes) the problem I have is he will moan (loudly) through the night, sometimes every hour. He isn't hungry as he just messes about on the boob. So I leave him moaning & he will go back to sleep. He is able to self settle.
But when my DD is here I can't do this as I'm worried he will wake her then I will have both to tend to . Is the inconsistency the problem? How do other people manage? Should I just carry on my routine whist DD is here & suck up a few bad nights?
Any advice please?