Oh you poor thing I do sympathise. It's horrible not getting enough sleep.
DS2 (now 4) used to be a nightmare at night, he slept through the night only a handful of times before he was 2 (and for 9 months of that time I was pregnant with DS3!)
It does get better though. DS2 is wonderful now and although DS3 wasn't even nearly as bad as DS2, he still had his moments, especially with the leaving him to go to sleep on his own.
The key is to be firm and consistent. It is sooooo hard not to give in when you are so shattered yourself, but honestly, if you stick to your guns and tell them every time they come in at night, 'This is mummy's bed, you have to sleep in your bed' and take them back, eventually they will get the message.
You need to have time to relax yourself and if you can't even get time while you are asleep it drains you. Blimey, my DH could tell you that on many many occasions I have woken up in a terrible mood saying 'I don't even get 5 minutes peace when I am asleep!!!!!'
DS3 will now settle into his bed and go to sleep alone and rarely comes into our room at night. Ds2 tries the old sneak in with mummy trick sometimes, but we laways put him back and because he knows the score he doesn't kick up about it.
Just keep putting them back. It will mean a week of not a lot of sleep but it will be worth it in the end.
Take care and I hope you get some sleep soon x