sing4peace, there is a Friends of Northampton Arsons group (or some name like that) on Facebook and United Way in Noho is handling donations. Here's this from the Boston Herald:

The United Way of Hampshire County also hopes to raise at least $20,000 for families affected by the fires, and the Red Cross is accepting money, clothes and other donations.

I am sure you'd probably find more in the Hampshire Gazette (the paper in Noho) and/or the Facebook group.