Rubbish sleeping 15 month old TWINS

[StillCounting123]

Just that really. Naps are hit and miss now, although up to around 12 months they were brilliant.

Twin1 only ever goes to sleep at 11pm (I fucking know) and wakes at least 3 times per night, sometimes more.

Twin2 goes down around 7:30pm, but can be up around 5 times each night. Sometimes at same time as Twin1, sometimes not.

I can't leave them to cry as they will set each other off.

What the hell do I do? On the brink of insanity, and have 3 other kids to deal with all day too (I'm a SAHM).

No ideas as I'm in almost exactly the same boat.
My DDs are 14 months. No space to separate them and not bubbled with anyone to give DH and I a break. I only have one other child though, I can't imagine what having more would be like.
I've had an average of 2 hours sleep each night for the last 3 nights. I'm on the edge.
We even resorted to leaving them to cry, 1 hour and 45 mins later they were still screaming. I don't know what to do anymore.