Hello, I don't have twins but I went through a similar situation so maybe this could help? The #1 best advice I read was to put your baby in the crib *awake* at bedtime. I started this when he was 6 weeks old, he wouldn't cry at all, just chill out or already be drowsy and go to sleep. Not perfectly every night, but there was rarely any fighting sleep.
Well, at 4 months he went through a developmental spurt (way more alert, no more long afternoon nap, grabbing things, etc-) and off and on for 3 weeks, he'd cry when we put him down! So we did a similar thing to Ferber, but we went in and comforted him as often as we wanted to. Just never picked him up and rocked him except for a couple super-fussy times, when I nursed him again. After those crazy weeks, he was back to a peaceful routine that has pretty much remained to this day, unless of course he doesn't have a good afternoon nap and then is a wee bit overtired.
As you go back and forth to check on him, keep an ear out - often, you'll hear the crying slow or be muffled as they start sucking their binkies or thumbs or just nestle in tighter; and their eyes will be shut...to the point that if you DO walk in, you'll make him cry more because he's on the way to sleeping, by calming himself down more. Soon you'll get the hang of it. (A good way to distract yourself from the crying is, in between checkins, work on chores or start dinner or whatnot so you can handle it - it is tough to hear!)
Much research speaks to the fact that as long as you give your kids lots of love, care, and attention, this crying will not damage them long term. As long as they're fed, not sick, clean diaper, etc., they're okay. And I know EVERYONE says this, but truly, my guy is good natured, and is overall a happy kid. What I realized is, as adults we can go for a walk, work out, gossip with pals, watch a funny movie, etc, to work off steam; a baby really just has crying, especially if they can't run/play yet to work off excess energy. Sometimes it seems to me that my boy is just venting or letting off steam. He's wanting to sleep but maybe still wants to play, maybe he is working on a new skill and he's overwhelmed by it, or is overtired, etc. As long as you're always checking in to comfort him in the crib instead of leaving them alone to cry it out, they know you're there and they have that security. And they are already good sleepers through the night (I agree you could even skip the 3am feed - my guy sometimes wakes up at 3am to vocalize and play, I just change him and replace the binky and say good night - it usually works, he often is back asleep in 10 min) so you're well on your way to a good sleep routine.
A good guide we used was Sleeping Through the Night, by Jodi Mindell. Similar to Ferber but not as structured. Beware, though, that a lot of experts want you to think that then your kid will ALWAYS go down easily and ALWAYS sleep through the night, but they evolve from time to time and that's normal - sometimes we push his bedtime back for awhile, for example; or if he's hitting a growth spurt he may wake once a night to eat (he was low birth weight). So far though nighttime is pretty mellow, and will be for you too! Good luck!