Hi Beamae - congrats on your babies 
I've got nearly 5 month old b/g twins and also a 5 yo DS and a 3yo DS.
I totally agree about aiming for a sequence of events rather than a routine dictated by the clock. I think that you picking random times for things to happen is unlikely to work well tbh. However, aiming to put them down for a nap 2 hours after they woke, and feeding 3 hourly, is reasonable and achieveable
Mine have fallen into a good bedtime routine without a huge amount of conscious effort.
DTS gets tired first as he naps less in the day, so he goes to bed at about 6.30pm. He's still swaddled and I bfeed him in his room in the dark before putting him down, as he finds it hard to switch off amidst the chaos of downstairs.
DTD is a more laidback character and will also take a bottle, unlike DTS, so she has one at bedtime. She goes down at about 7.30pm usually, either by falling asleep in her bouncy chair or being put to bed awake.
Daytimes vary but I do 3 school runs a day so that gives some structure. DTD definitely needs more sleep than DTS, but the flip side is that by evening he can be overtired and goes a bit crazy.
I guess I'm trying to say:
In 99% of cases a bedtime routine will evolve without much effort from you -it just happens as they get a bit bigger, and also,
that you may find that your twins are very different - mine are. What suits one might not suit the other. Be prepared to be flexible on this. Try not to compare them too much.
DTS is very similar to DS2. DS2 was a huge shock to the system as DS1 was very easy. I spent hours trying to settle him in his cot. He hated it, I hated it and it was miserable for both of us. When I finally gave up and took him into bed with me, it was so much nicer for both of us. By about 3 months though, he went into his cot very easily, and I wished I hadn't battled so much when he was tiny - he clearly just wasn't ready for it then.
Fast forward to DTS and he's so similar. Yet the experience I've had with him has been so much nicer as we've just gone with the flow. For the first few weeks he was attached to me or swaddled super tightly. He came into bed with me if he wouldn't easily settle back into his cot at night, which was most nights. Now though, he sleeps on his own very happily and as long as he's not overtired he's a happy little chap. I think of him as a much easier baby than DS2, but in reality he's not that different. I think I just handled it better and changed my expectations.
Life with twins is hectic, so go easy on yourself. A routine WILL evolve when they're ready, despite what some of the books imply, but trying to push them into something they don't want to do will make everyone miserable.
Some aids to help the babies self settle are so worth it too, as you can't see to them both at once. Swaddling has been a godsend for DTS. DTD loves her dummy and swing chair. If anyone is allowed to 'cheat', it's us twin mums!
Enjoy them. The tough sleepless part is not for ever.
Oh, and don't get too hung up on the whole' XXlbs means they can sleep though' thing.
DTD was an angel and slept 12 hrs from 6 wks, and was only 9lb-odd at that stage. DTS who is 2 1/2 lbs bigger, has never slept through let. DTD slept through really well from 8-12 wks, but it's now gone out of the window nad she's up every 3-4 hrs round the clock - joy! Her weight has nothing to do with it!
HTH and sorry for the essay 