Cosleeping now will not condemn you to a decade of forced cosleeping w/ a child who refuses to leave your bed. I've coslept w/ all three of mine & the eldest two, ages 8 and 3, have moved on to their own beds and sleep very well on their own. No issues getting them out when the time came & they're normal, healthy children. Cosleeping is an awesome choice, if it fits your family.
I think the Ferber Method is crud. It may "work" but not the way I want my children to learn about sleep. Sleep should be a safe, healthy place, but Ferber pretty much just trains the child to give up hope that someone will come help.
Off my soapbox. :)
I'd try the Hiland's Teething Tablets. Check for ear infection. Cuddle her to sleep in your bed & when she stirs, cuddle her some more. Something's bothering her & momma's cuddles always help. :)
Are things too quiet for her? Can you try having a fan on for some white noise? Does she wear jammies? Maybe they are bothering her & keeping her in nothing but a diaper would help. Maybe she's hungry & needs a snack before bedtime? My ten month old will nurse all night if she doesn't go to bed with a full tummy.
Good luck! You've certainly got your hands full; I hope you find a way to get your girls & yourself lots of good sleep! :)