C.,
It sounds like you're ready for a fight every night and I'm sure your daughters can sense that. Research has shown letting kids cry it out can cause trust issues. I'm glad you're trying another method.
First, you've got to change your attitude towards bedtime. Start expecting that they will go to sleep without a fight. Establish a more consistent bedtime routine: Bath, teeth brushed, prayer, story, hugs and kisses, song and then lights out (or something similar). A story is especially helpful in providing an atmosphere where they can calm down. If you remain calm and reassuring the whole time that will help.
My 6 year old and 3 year old daughters share a room (bunk-beds). My 3 year old just turned three and still takes a nap during the day so sometimes she isn't ready to sleep at the same time as my busy 6 year old. We do the bedtime routine and then when the 3 year old gets out of bed I will keep her with me and read a few more stories while the 6 year old goes right to sleep. When I can tell my 3 year old is ready for bed I can then take her in her room and tuck her in.
I think it's fine if they want to sleep together. You could even move one of them to their own bed after they're asleep. Just make sure you're putting them to bed a little earlier because chances are it will take them longer. Don't get upset if they don't go to bed right away.
Hope this helps. Good luck!