Huf can be created widow wife as karta?

Dear Sir,

I want to know whether HUF Can be created in the name of Widow Wife i.e. Husband had Expires and he had not created any HUF in his name. In family there is only 2 Members i.e. Wife, Son & Married Daughter. Now I want to know how to create HUF with this members ( Wife - 57Yrs & Son - 32 Yrs.) I want My Mother ( Widow of My Father ) to be karta of HUF & Son will be member.

Is it legal & if yes Pls. attach all relevant documents required for HUF Creation.

SS.