E.-
How precious to have twins and to be able to stay at home with them. Congratulations! Being twins, I'd have to ask if they were born prematurely? If so, she might be having reflux symptoms, which flare up at night when lying flat. Or, like others have mentioned, if could be ear infection, teething, or simply a stage such as separation anxiety.
Whatever the case may be, I'd definitely have her seen by her doctor, first, and mention concerns about reflux (this is not easily caught by most doctors-in fact, my youngest daughter had all sorts of problems that were attributed to colic, anxiety, teething, bad temper, etc. until she was 4yo and was finally diagnosed with reflux, which explained every symptom she'd had!).
You can try propping her mattress on one end and seeing if sleeping on an incline helps her to sleep better/longer, but otherwise after seeing a doctor, do what she needs to be comforted and rest. For my son, he couldn't be soothed to sleep by any of us no matter what. Once he was agitated and crying, we'd simply have to let him. Rocking him, holding him, playing music, singing, swinging, etc. wouldn't only end up making it worse until he was so exhausted he'd pass out. He was like that for months, unless he simply fell asleep in the car! We took quite a few car trips at night gefore he was 1 (BWG).
And then you need to rest. I know that's hard with any baby, especially with twins, but it'll equip you to help them both better. I know they're not newborns anymore, but mom's need to be well rested at any age of their child to help them the best. And, if she's that distressed it will wear you out without realizing it. HTH and good luck!