Is it possible because NCR want them gone?

MAJOR SPOILERS:








There wasn't on House's quest line. So, I'm guessing no. However you can help some of them survive by getting Hardin to be elder, as this will cause a few scouting parties will be outside when you destroy the bunker.

Sure, just do the main quest for yourself. After killing house upload Yes Man and then you will end up killing both NCR and Legion.

I gave Ceasar the finger when he wanted me to destroy them. Then I high tailed it out of his camp. I didn't want to destroy the BoS due to their armour and such.

Yes. First, you have to leave McNamara in charge of the BoS when you do the quest Still in the Dark. Then when you do the quest For the Republic, you can convince McNamara to ally with the NCR.

No way to get Harden to align with NCR? Damn.

Do some side quests with that Brotherhood Scribe located at Trade Spot 188 near BoulderCity/HooverDam. [She's the companion choice with the full robe and powerfist].
Lead her around the populated areas, NCR controlled territories, and gang areas, she'll start coming up to you with dialoge until she finally asks to return to her home. Take her.
Same thing with the Boone quests really. She just requires a bit of exploration.

I ccan't guarantee anything because I haven't completed all of her quests yet though.

do i need to have a minimum skill level to convince him?

The strategy guide doesn't say anything about a conversation check, so I'd assume it is just a normal dialog choice.



Nope, the strategy guide specifically says that Harden will never ally with the NCR.