not enough info to give you a meaningful answer.
perhaps they think they don't owe it to him? A funeral costs anything from £2000 upwards. If they had no money (it's not like a house actually represents "money")then why wouldn't your b/f want to pay for his mum's funeral? if the 6k was from her will/assets then paying for a funeral should have come first anyway, before anyone got any payout
Also the dad has been housing him for 2 years (is he paying rent?) if not it would have cost the b/f more to pay rent than 6k for 2 years
This answer is based on the 6k being from a will/intestacy and the dad not charging any rent (which i have completely assumed) if the facts are different , please accept my apologies and re-post