I am still breastfeeding mine, who are 4 months old now.
I found it massively difficult in those early weeks. One of mine had a problematic latch, causing bleeding and cracking if I didn't work really hard at retraining her. (The worst bit about that is that with a singleton you can rest the nipple for longer, but with multiples it is like a constant onslaught with no let up.)
These were babies 3+4 for me, and I felt like with dd2 I had got the hang of breastfeeding and coping with lack of sleep. Having the twins really took me back to square one and I had to learn new things all over again. I couldn't use my fallback methods of soothing and feeding by using a sling or feeding lying down. I hated feeding them both together, (still don't really like it to be honest), but with the constancy of feeding in the early weeks it became essential in order to do it all.
I was really keen to breastfeed initially because for me, I knew it would mess with my head in the long term if I didn't do the same for the twins as I did for dd2 and dd1. But honestly, I was ready to crack open the formula within the first week, it really did test me.
I don't want to go on and on here about myself, I just said the above to try to show you that I think I know something of what you are going through. I don't think I had it as tough though, because I had someone staying with me for the first 6 weeks, then after that dd1 was in school and dd2 was in nursery for 3 days a week, so I only had 3 children for 2 days a week.
I do think it is worth trying to push on through this tough phase, because now it is sooooo much better and I am hugely glad I am still breastfeeding, even though I knew formula wasn't poison and really probably wouldn't make any difference at all, it was just something I wanted to do.
I always fed them simultaneously during the day up until about 3 months, when their feeds sped up so much that I could do them one at a time very easily. I now don't find it any more trying than having a singleton because they are happier being awake and looking around (so don't cry when the other is being fed) and each feeds in under 15 minutes.
Reading your op, do you really have a problem with the breastfeeding or with them not having proper naps?
Breastfeeding:
Are you confident they are latching ok and draining your breast properly - are they properly full when they finish? Do you think they want feeding more often than three hourly? Could it be they are too little to last that long yet? I wonder if they would be able to cope with the delayed letdown if you fed them a bit earlier ie before they were too hungry? My feeling is that such a rigid routine is a bit early for them at such a young age, but I am not very routiney.
Rest:
Are you only getting out for a walk for that half hour in the afternoon? How do they sleep in the pram? If you don't have your other child to look after could you take them out for a long walk when the weather is ok, and put some music on your ipod and take a flask of coffee with you? If only one baby is struggling to nap, could you put him/her in a sling to get them to sleep?
I managed to go to the parent and baby screenings at that young age - it's difficult but doable (just). Is that an option? If you take lots of padding you can put that on your knee for their heads then use the arm rests for their bodies and feed them at the same time...it's probably best to do this first time round with someone else there for moral support.
What help do you have? Could you afford to get some help in for the next 6 weeks, just to take them out in the pram or whatever so you can get a break?
My final word. I promise. I do think it is hard for every multiple mum in those early dark, dark, dark weeks. I don't think you can lay that entirely at the door of breastfeeding. Formula feeders don't necessarily nap well, or feed quickly, so it may not be the magic bullet you are looking for.
Good luck, just do your best, and then if you really want to add the odd bottle, at least you will know you reached your personal limit and could do no more so will have no regrets.