Yes, Mary I have been there. My dd was 27-months-old when her sisters were born. I knew that she would probably have a tough time adjusting to "twin shock" but still wasn't fully prepared with how it would make ME feel to see what she was going through. I did some preparing before the babies were born and got together a basket of goodies for her (with the help of my wonderful LLL Leaders!). I filled the basket with trinkets...puzzles, books, dolls, crayons, play-doh, stickers, etc. that I bought various places. The Dollar Store was great for this! On days that were particularly hard I would pull a goodie for her out of the basket and it was like a little piece of gold for her. It's not too late to get a basket together for your son.
Other things I did were to spend as much time as humanly possible with her without the babies. If they were napping together - even if only for 5 minutes - I would make sure to do something with just her. Swing on the swing set, read a book, color, let her help me cook something, etc. Also, I know it's tempting when DH gets home to let him take over with your son but maybe you'd want to let him take over with the babies instead. Do some one-on-one things with your son wheh Daddy gets home. That way DH gets some time with the twins and you get some time with your son. You could nurse the babies and hand them off to your DH and then take a walk with your son.
The worst part of it all is for you to have to see what he is going through. That is what absolutely broke my heart for my dd. Here she was barely over 2-years-old and already having to do so much for herself. I look at my twins who are now older then she was when they were born and think of what babies they still are. It makes my heart ache for how quickly she had to grow up. Do all you can to make sure that your son is able to stay "little" as long as he can.