Yes, absolutely supplement with formula (if your doctor agrees) if it gives you some relief.
Sisi never developed as good of a latch as Greenbean. And her suck was weak, very much so in the beginning. When one got hungry I ALWAYS fed both. I used the EZ2Nurse pillow which is WONDERFUL (was told about it here) and always fed both at the same time. One big plus to this is that Greenbean had a strong suck and I felt that because of his strong suck, I produced a lot of milk on both sides. Sisi always got her fill and I think it was because of Greenbean's strong suck on the other side. Not sure if that made sense. I don't think she would have gained the weight she did if he hadn't had such a strong suck because she couldn't achieve a good let down on her own.
But, in the beginning, when they were so tiny and so very tired, neither wanted to eat. I would try to nurse, then try to pump to keep my supply up until they got stronger, and then dropper feed them formula. After a few months, they got stronger and stayed awake for feedings. But man, that first month was so hard.
Hang in there, you are doing great. Congrats on your new twins!
" I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent." Mahatma Gandhi
"This is the ultimate weakness of violence: It multiplies evil and violence in the universe. It doesn't solve any problems." Martin Luther King, Jr.