Well, for starters, the two youngest should have a much earlier bedtime than the two older ones. The toddlers should be hitting the hay closer to 7:00 pm. The older ones can probably stand to be up until 8:30 (unless they have a super early bus pick up on school mornings).
So, you let them cry (if it comes to that) at bedtime--not necessarily during the middle of the night. There is a big enough gap in your kids, that you NEED to have different bedtimes for the two age groups. Yes, that means more "bedtime work" for you and husband, but that's how it shakes out sometimes. Different kids have different needs.
Jo W. is right on the money that the biggest issue you have to face is that your kids do not know how to fall asleep without using you or dad as their security blanket. They need to learn to fall asleep in their own bed--not on the sofa with either of you, or in your bed or anywhere else--- and not with you IN the bed with them. Otherwise, guess what they will require to fall back asleep if/when they wake up in the middle of the night....
Get that issue resolved first, and then you can work on the middle of the night stuff (which essentially amounts to you walk them back to their rooms each and every time they come to you during the night---with minimal [none if you can do it] eye contact or talking; And you don't carry them, you make them walk).
There are a lot of ways to go about getting them to go to sleep in their own beds. Your 10 and 9 year old shouldn't require much more than you telling them there is a new bedtime routine and here it is. The younger two, there are tons of books about how to approach it, or just search on this site for "how to get toddler to sleep in own bed". In our house, I used the Ferber Method to get my daughter to learn to fall asleep on her own. At 6 months she could fall asleep in her crib, alone, without any crying--and she slept all night. Other people have other favorite methods. Check around for what you are willing to try. And when you are ready, try it... and stick with it long enough to give it a real chance. If you try something new every 3 or 4 days because the first way "wasn't working", then you aren't giving a fair chance to the method involved.
Good luck.