For me there is no issue of self defense.
The young men were invited in by the daughter who lives there.
The young men did not threaten or attack the father.
I would have ordered them out and told them not to come back.
Than I would have communicated with my daughter in private.
No reason to draw or threaten to shoot because there was no attack or reason to think there would be.
Little different if you come home and hear your daughter screaming and being attacked.
Not the case it seems here.