Schedule, schedule, schedule! If you get them all on a schedule, you will have more time than you know what to do with. I am a foster mom and I currently have 3 kids, 2 of which are babies. I sometimes have 4 kids, and we only take the young ones so things can get a little crazy at my house.. I always get them on a schedule the minute they come into my home and they adapt very quickly and are a lot more calm because they know what to expect. I also have a 4 year old biological son and I put him to work helping out which he loves because it makes him feel important. He can put waffles in the toaster and pour milk for himself and the 12mo old, he can bring me diapers, put laundry in the hampers, sort clean silverware, etc. If he is busy helping, he can't get into trouble. :)
For Infants 0-4mo old, I always put them on a 3 hour feeding schedule. They wake up, eat, play, sleep, repeat. I wake them to feed every 3 hours during the day and then let them sleep away at night. My son slept through the night at 6wks old on this schedule, my foster babies that are older than 2mo old when placed in my care are usually sleeping through the night within 3wks of being on this schedule at my house. With this schedule, they eat 6-7 times per day which is exactly what they need. It also helps any tummy problems because they are up after feeding which helps move the air out. If they are sleeping right after feeding, it can cause all sorts of tummy issues. I also always lay them down awake and let them fall asleep on their own which helps them learn to self soothe, no I don't do CIO - on the schedule they know what to expect and they sometimes get fussy if I keep them up past their nap time - they like their naps!
For ages 4mo - 6mo, I stretch their feeding times to every 4 hours (since they are eating more) and give them 3 naps per day. For ages 6mo - 12mo, I keep their feedings to 4 times a day, breakfast, lunch, snack, dinner, and they nap in the morning and afternoon. Ages 12mo and up stay of the same feeding schedule but go down to 1 nap in the afternoon. My 4yr old isn't required to nap but he does have quiet time so I usually get at least 1.5 hours of quiet time in the afternoon to do something for myself.
All kids are in bed by 8:30pm, and because they have learned to put themselves to sleep I don't usually have to deal with fussiness. Bedtime routines are short and sweet and happy.
If your kids aren't used to a schedule it will take time to get everyone on it but stick to it and enforce the rules and soon you will have some time on your hands.