I have 4 1/2 year old twin boys. My boys were in the NICU for a bit and we had to feed them every 3 hours, 24 hours a day for 8 weeks. We were not able to start sleep training them until they were 2 months old. It took another 3 months to get them to consistently sleep 5-6 hours at a stretch at night. By the time they were 6-7 months old, they were sleep 8-10 hours a night and by 8 months, they were sleeping around 12 hours a night.
My recommendation is this: Put them on a strict routine. When one feeds, feed the other. That means you might have to wake one up at night. At this age, if they cry because they are tired, you've waited a little too long to put them down for a nap. Try to catch them before they get overtired. We did a routine during the day of eat/play/sleep. They would wake up around 7am and by 8:30-9am they were ready for at least a 2 hour nap. When I KNEW they needed to sleep, I would put them to bed (in their cribs), give them a quick snuggle, and leave the room. Don't linger. Sometimes I had to go step outside so I wouldn't hear them cry.
Routine, routine, routine will get you where you need to be. If you can get 4 hours of straight sleep, you will feel like a new woman!