Hi H.
I have an 8 year old boy, 7 year old girl and 8 month old baby girl. As much as I wanted to let my older kids sleep with us at night...I never did/never will because I was afraid to start a tough 'habit' to break. And so far, we are keeping the same routine with my 8 month old. My son has come into my room in the middle of the night 2-3 times EVER from being spooked, but he always wants to go back in his own bed because he has grown up happy and comfortable in his own room. My older daughter, however, used to get really scared at about 5 years old and was constantly trying to sleep in our bed. I know it may sound cruel to some moms, but I never let her (again, didn't want to start a habit that was hard for her to break). Instead, we put a VERY BRIGHT (but safe) nightlight in her room and helped her fall to sleep by sitting in her room. Noises were never a problem for her, but I know sound machines are a great way to provide some white noise and drown out the 'scary' noises your daughter may hear by finding a soothing noise. After a few months for my daughter, the nightlight was able to dim down a bit and she is a great sleeper now. She still likes me or my husband to sing to her/scratch her back as she is falling to sleep, but we are (always have been) very happy to make her (and her brother/baby sister) feel safe/cozy as she is going to sleep.
If I were you (and this is only my own opinion), I would make a "house rule" that everyone has to sleep in their own beds. I might give stars/rewards for every night they do it...maybe a big prize (big in their eyes) after 3 or 5 nights in a row. I would do whatever it takes just to get them used to it, and that could be brutal for several nights. But the payoff will be huge for your family....mom and dad get to sleep together by themselves and your children learn to become good sleepers. Everyone is better rested and bedtime is no longer a dreaded anxiety for anyone!
If it is just too heartbreaking to go cold turkey...let your kids come into bed in the morning (after the sun comes up!) to cuddle. Gradually move those mornings to Sat/Sun so that the weekends become an extra-special time where you can all climb into bed in the mornings and cuddle. You could also let them have "sleepover nights" with eachother on the first night and then the weekends. But I probably wouldn't have it every night or they may have a hard time becoming independent sleepers. Again, it's just my opinion. It may be really hard for a bit, I would say "everyone has to sleep in their own beds" as a general rule and then give them the tools to be able to adapt (bright nightlights, sound machines, cuddle-mornings, etc.).
Best of luck to you with whatever you end up doing.