Party

Sensory balls, stickers, snacks (depending on dietary restrictions), bubbles.

There are tons of great ideas for little ones on the Spectrum. Depending on the severity of the kids sensory issues you may want to be sure that your party is not over stimulating. Keep decorations from flapping around (ie. crepe paper streamers or stinging ballonns in places where the wind will catch.) Keeping games from being too loud and keeping the ratio of kids to adults at a good level for someone to be able to deal one on one if the need arises. There are lots of good (cheap) ideas for party favors that include everyone but are things the autistic child will actually enjoy. Check ebay under speech toys for some great ideas (that can be bought elsewhere). I also included some sites that cater specifically to toys for autistic kids. There are some little things than can be picked up in sets. Also, it can give you ideas of items you can buy from the dollar store later. Hope this helps. Any other ?'s please feel free to ask me privately. I have a background in special ed. and I am a clown on the side. I am also our church Special Needs Ministry leader.

http://www.toysforautism.com/ http://kidscopetoys.com/ toys.shop.ebay.com/Educational-/.../i.html?_nkw=autism+toys
www.ozmofun.com

I guess I'm a little confused. A child(ren) coming to your twin's bday party are diagnosed on the autism spectrum.
I guess my first response, is don't treat any child any differently if at all possible. That being said, you do have to make accomadations for some things - like diabetic, etc. With an autistic child, speak to the parent and see if they have any sensory issues etc and go from there. But I would strive to make the same bag for them as the other children.

Foam alphabet/number/shape puzzles, touch a bubbles, bright coloured stuffed animal with a neckerchief tied around it with their name on it, small toy kaleidoscopes, cardboard tubes wrapped in coloured wrapping paper or fabric and the ends twisted and tied off with ribbon on the end to look like a giant candy...they can be stuffed with beans and noodles to make different noises.
Cardstock or a paper plate, and foam stickers, small picture of the birthday kids(If you have your own printer, grab pics of the other children with the birthday kids at the party to go into each personal bag), a cup of various shaped noodles/beans to make their own party memory scrapbook page.