Need advice

[Great-Kazoo]

I don't know if she will press charges and he knows I carry a pistol everywhere. He is nervous about me not that I'd ever un-holster.

he is a former felon

X police dispatch how may i help you. yes there is a man with a gun threatening my sister.
UNLESS she presses charges, she will never leave him AND more than likely sign a deposition / statement against you, taking his side.
It sucks, but until she chooses to make the next move your hands are tied. Now if you happen to "walk in" while your sister is being attacked that becomes a game changer.