If we could figure out why pregnant women have the feelings they do then we could both be millionaires! lol. If you don't feel like it, then you just don't feel like it. You can't force your body to do what it doesn't want to do. Perhaps your hormones are down, and you just don't feel it. Perhaps a part of you is resentful towards him.
Now that's not to say that you can't try. Your husband sounds very understanding and very sweet. Let him know that you want to try, but that it might now work, so he doesn't make you feel pressured. Set up a romantic evening, whatever it does that makes you feel romantic, slow music, dim lights, and have your husband give you a full body massage. Or you can sit/lay and cuddle on the bed or the couch and just enjoy being with one another and talking.
Remember that you have nothing to be insecure about and that your hormones can make you feel this way. Make sure someone is watching the twins so that you can feel like you are free to be yourselves and not worry about them. It's just as important to touch, cuddle, caress and give each other love as it is to make love.
I welcome your thoughts, let me know if you want to talk more