My brother had an accident 5mo.ago which he had lose his teeth, 5mo.later and his gums still bleeding, what might cause, ?

Needs evaluation: Have your brother see a dentist. There still may be broken roots, or the teeth that are remaining may have problems. All the best...

Bleeding: Are his gums bleeding where the teeth were lost, or are they bleeding around other teeth in his mouth? There is no way to answer your question without a physical examination. Your brother must see a Dentist immediately. Prolonged bleeding is not normal, and can signal anything from infection to systemic disease to neoplasm. See Dentist now.