We've been getting much better sleep with the babies lately. At the very beginning, they only slept for about 2 hour stretches. By around 4 months, this had gradually stretched out so that they were sleeping for 6 hour stretches or longer. Then, Miles started waking more frequently - back to around 3 hour stretches. Jason and I were exhausted again. We couldn't really figure out what made him start to wake up again. "They" (whoever "they" are) say that they start to wake more frequently at developmental milestones, when they start teething, etc. But we never could figure out the cause.
While we were at my parents' house, they started sleeping very well again. They usually go to sleep around 6:30 PM. They (usually Miles) wake up to eat anywhere between 3 and 5 am, and then usually sleep through to around 8 AM. Of course, there is slight variation in this pattern, but this is generally what our nights look like now. It is so nice to be back to single feeding nights.
At my parents' house, they also started taking very good naps. When they were younger, they would often have their daytime naps in their bouncy seats or nap on us while we slept with them in the recliner. Just over the past month or so, I've been putting them down in their cribs for their naps. Actually, I put Miles in his crib in the nursery and put Vivienne in the pack 'n play in our room so that whoever wakes up first doesn't wake the other one up with their crying.
At first, they did not nap well in their cribs at all. They were gradually getting better, and then in Georgia, Miles napped for about 4 hours one day. I was shocked! Since we've gotten home, they have been napping well in their cribs.
We started letting them cry a bit more over the past few weeks - not exactly "crying it out", but letting them cry for a few minutes before we go in to comfort them or feed them. But usually if they cry for any more than 15 minutes, I will go ahead and feed them. We were worried that we might be teaching them that they can cry any time, and we will come running to feed them, but they seem to be learning to soothe themselves well. Miles and Vivienne both suck their thumbs, which I've found to be very helpful. They can soothe themselves with their thumbs, and it's also a very clear indicator to me that it's nap time when I see them popping their thumbs in their mouths.
We don't do any particular kind of sleep training. I just try to listen to what the babies need. Sometimes it's very difficult to figure out what they need, but usually they will tell us if we focus on their cues. I think we honestly just lucked out with good sleepers.