Sleep deprivation/disruption is literally killing our sanity, sex life and marriage!

Sleep deprivation/disruption is literally killing our sanity, sex life and marriage!
We have 3 kids under 5. The eldest 2 are driving my husband and I insane. They are 4 & 3. We have always stayed beside them until they fall asleep (in their own rooms). For the past few months, 4yr old will come into our room every 1 to 2 hours! We take him back to bed, lay with him till he goes to sleep, then we do it again an hour or so later. Now the 3yr old has started this too.
So our house is like musical beds. Sometimes I’m in our bed, hubby stays up later, he intercepts child, ends up in child’s bed. 3yr old comes in to me, I take 3yr old back, lay down, get back up and go to my bed, sometimes hubby is there, sometimes the 4yr old, and around we go ALL NIGHT EVERY NIGHT. Suffice to say we are getting increasingly less sleep, hubby and I are always cranky and exhausted. Kids are a bit out of sorts.
They go to bed at about 7pm every night, same routine as forever. This all started when the eldest started wearing undies to bed and would start when wakes for the toilet. Now it is purely habit. Thank goodness little princess sleeps ALL night. So far.
We are desperately seeking other people’s success stories and or idea’s on how we can put an end to this. Please no obvious comments about how it’s our fault. We know and own it. We need constructive help that will work. Thanks