Op- my twins were exactly the same at 18 months. Cutting incisors and the 18 month developmental growth spurt were utter hell for us.
Dr Jay Gordon/No cry sleep solution are worth reading. And I found natural mamas forum helpful and I signed up to an American ap twin list (I have no intension of ap, it just suited my twins sleep needs).
Are your twins ID I found a couple of studies about how much more sensitive ID twins are to pain and my twins really struggled with teeth pain. And silent reflux (still do as big kids) and CMPA.
In the end, after those incisors and that growth spurt I put them in cots with a mattress for me in between them and stayed with them and held hands and shhhddd etc but refused to feed until 'morning' which was allways around 4 am. .... (still is, but they have asd etc and still don't sleep much)
They did cry, but we're never left alone. And it was hard for me to hear but it was possible I think because I could lye down in comfort and not worry about getting back to 'bed'. I was close enough to cuddle them lots but the cot meant they could just roll over and latch and it gave a clear boundarie that nursing in bed was no longer an option. (Although I nursed and slept in the big bed for the 4 am marathon bf).
They seemed to like having their own room, and we still keep a mattress between their low beds to settle them to sleep. Black out blind, white noise, my fluffy dressing gowns for blankets and non spill water cups in cots were used. They bf til three ish so night weaning didn't effect that.
I wasn't bf them to sleep at 18 months though, around 1 ish oh took over settling them to sleep while I slept down stairs, ear plugs in. So they already could fall asleep without bf, just not resettle them self's until we night weaned. Oh said they cried a lot, but it only took a few nights and again they were never left alone, allways cuddled and comforted just not by bf.
I hope some of this helps you some or gives you ideas. Modeling healthy self care is important also and you will know when you can't take anymore. Best of luck.