We've been in a pretty similar situation. I don't know how you do it with two though, looking after one child is enough for me on such broken sleep!
We went to a MCHN sleep school at about 4 months, which helped a little but we slipped pretty easily back into feeding and cuddling to sleep, it just seems so natural to me and sooo much calmer, I got tired of battling for every 20 minute cat nap.
Up until recently DS spent his day naps asleep on me while I was parked on the lounge, but after a bit of work he now naps in his cot, it's mostly the nights for us that are horrible now. We did have some improvement about a month ago following some advice from Karitane, but things have gone backwards again. Every time I go to lift DS up over the cot rails he arches his back and loses the plot. He gets so worked up that nothing will calm him down. I hate seeing him so upset, I usually end up in tears too.
DS is the same as your DD too, very clingy to me and won't let my DP settle him. It's a lot of pressure and stress on us.
I'm not even sure any of my post makes sense, too damn tired, and DP is lying next to me snoring like a bear.
Hears hoping we all get some decent sleep tonight.