Can two married sons form a huf?

Not very difficult, provided father left any asset.

if he died intestate, can huf be formed?

 HUF is purely  a creature  of law and cannot be created by an act of parties. A HUF is a fluctuating body, its size increases with birth of a member  in the family and decreases on death of a member of the family. 

No question of will or intestate; as thats for individuals. Any property acquired by the Hindu great grand father, which then passes undivided down the next three generations up to the present generation of great grand son/daughter.

Refer: https://www.itatonline.org/articles_new/the-entire-law-relating-to-hindu-undivided-family-huf-explained/