I have a 5yo who goes up around 7ish and is asleep (or in bed on her own at least) by 8 latest.
I have a 6m old BF baby who until last week would always be in arms during DDs bedtime, would feed and come downstairs with me for mine and DHs dinner, (sometimes asleep sometimes awake) before I'd go up with DS at around 10ish.
Randomly last week I got DS to sleep on his own, (BF and crept away) had a lovely bed time with DD just us two, it was wonderful, then had an evening downstairs with DH, we had a glass of wine, dinner with two hands and even read a bit of my book.
I WANT TO DO THIS EVERY NIGHT NOW 
but DS and I can't seem to sort our shit out.
I've tried getting DS to sleep early so DD and I can play for a bit, but then he wakes just as DD and I are reading a story, I've tried giving them both a bath, taking him out first and trying to feed to sleep, then she comes in to his room, and wants a nice bedtime (understandably) but then she wakes him up and it all goes to shit...
Tonight I got him to sleep early and he woke while I was reading a story, then wouldn't go back to sleep, I gave up and have brought him downstairs but he's moany and rubbing eyes so he's obviously tired but the little bugger won't actually go to sleep.
Salient facts - I do have a DH but he often gets home late and I need to be able to do this on my own. When he is here he takes her and I sort DS out. I ebf and don't leave him to cry, we co sleep so he's used to me there, his naps are shit in the day but we have a very loose routine of naps at 9.30, 12ish, 3ish and 5ish...
I know it's all a phase and there'll be something else in a few months but right now I have NO IDEA what I'm doing and how to let us all have a nice evening. I'm finding things quite dispiriting right now.