I would feel okay with it in very certain circumstances, but not at three months, and not with babies who are still so small.
I understand your dilemma-- I had boy/girl twins as well, and DS was severely casein intolerant, soy allergic, and refused the hypoallergenic formulas. When he stopped gaining weight, I was at the end of my rope about how to get more calories into him (this was between 4 and 6 months). There was an enormous temptation to resort to something like coconut milk, or hemp milk. I thought, oh, just a few ounces a day won't hurt. But everybody here talked me out of it, thankfully, and what we ultimately did was to embark on a massive supply-increasing campaign. I started nursing them each individually, alternating who went first each time. When each baby was nursing, I had the pump on the opposite side. Then nurse the other baby, and put the pump on the side baby isn't on. Then repeat--- around the clock. Of course the second baby didn't get enough, so we had to nurse again within a half hour or an hour, whereupon that baby got to go first, and we repeated the whole scenario. It was HARD HARD HARD, but within a week, my supply had SOARED, and I was satisfying both babies, plus pumping out fountains of extra milk that I could put in DS's SNS to boost his weight gain. By six months, he'd jumped the percentile chart from 15th percentile to 50th, and I had a freezer stash I'd never aimed for.
Sometimes women have trouble pumping enough because their bodies aren't responding to the pump the same way as to baby, and that's why you pump one side while nursing on the other. That way baby elicits the letdown reflex for you, and all the pump has to do is extract the milk. Remember, it's frequency that matters most-- nursing more often, and pumping more often, even multiple times within a short amount of time, and even if the breasts feel "empty." It's normal for them to start wanting to nurse more often, during the day and night, while you're starting a pumping routine-- that's a natural part of the process, as they cooperate in increasing the demand. If you REPLACE nursing with pumping, then you will be taking calories from them, but if you ADD pumping to the nursing, they will be fine. And the extremely frequent nursing should decrease as your supply responds.
So here's my take: The first thing would be to attempt more drastic measures, to increase supply. Right now, you're making just what they need, but if you increase demand drastically, and consistently over time, the supply should respond. In the majority of cases, mamas will see the supply meeting the demand, within two weeks or so. If that doesn't work out, or it seems too overwhelming (and trust me, I know what it's like to live with twins!!!! So I am not judging AT ALL. Remember, I tried four types of formula before I got to that point!), I would resort to commercial formula. I don't think I'd give alternative milks to such a young baby, for three reasons: 1. Goat's milk is not nutritionally complete for a human infant, and at this age, they are at a very sensitive time in their development, 2. any supplementing at all is a downward spiral, so it's possible that over time you may become increasingly reliant on the goat's milk, which could mean that 3. baby is getting too much incomplete nutrition, which reduces baby's appetite for breastmilk and means baby isn't getting the nutrition needed for development.
I am not a big fan of the homemade formulas, but if you truly want to give a goat's milk, it may be a good idea to look into how to add to the goat's milk to make it more complete. Again, I am not recommending this-- a commercial formula would be my preference in this case-- but be aware that it may be a better option than just plain goat's milk.
Best of luck to you, whatever you decide.
for you and your DH and your job for working all that out
