There are many organization working specially for twins,

Twinsmagazine     http://www.twinsmagazine.com

Twinsonline           http://www.twinsonline.org.uk

Twinsights               http://www.Twinsights.com

The international twins Associations

Twins & Multiple Birth Associations (TAMBA) -UK

The Multiple Births Foundation 

Twins Advise

City of Twinsburg

The Worldwide Twins and Multiple Births Foundation Inc.