Disclaimer: This is a serious enough issue that in a lot of circumstances, it would be appropriate to kick this player out. I can see why that's not your first choice here, but just know that you may not find a perfect solution.

Situation

Here's what I'm getting from your question:

• Your dad used to play DND in college (presumably a while back.)
• He plays as if the ends justify the means - he doesn't expect to have to be nice to people if he's doing it for a good cause.
• He kind of has this attitude in other areas of life as well (we try not to psychoanalyze people over the Internet, but you brought it up more than once, so I'm taking your word for it that this is relevant.)
• Family dynamics are complicating the game dynamics.

Based on the above premises, I'm not going to suggest you have a big Talk About His Behavior; for one thing, you already have and it didn't work, plus you're concerned that he'll interpret that as a personal attack, and you know him best. So I'm going to suggest something a little unusual for the problem-players tag: Let the Wookiee win. By that I absolutely do not mean let him steamroll over you and the rest of your players/family and continue to make the game miserable for all of you. But I do think you need to apply a principle that's as true of RPGs as anywhere else: find what works, then do that. More specifically, I think it's worth trying to find a play style that he can be fundamentally happy with, and then seeing if you can accommodate that in a way that's still fun for everyone else.

Find the Fun

So, what does he want out of this game? I can't tell you that. You might formally ask (as I've done in this survey of player motivations), or bring it up more casually, or employ trial & error and see how he reacts (not my preferred option but may be necessary if you're not confident you can have a productive conversation about it.) Ideas to get you started:

• Blowing off steam/escaping from stress into a world where things go smoothly, your decisions matter, and you're able to exert influence over your environment
• Challenge/escaping from boredom into a world where things are exciting (not as contradictory with the last point as it sounds, though there's certainly a balance)
• Recognition - being famous, admired, greeted by cheering crowds, etc.

There are many more motivations for playing RPGs worth exploring, but I highlight these three because I have a hunch, based on the information you've given, that one or both of these things are true:

• Your dad is used to playing in a more straightforward dungeon-crawl/hack-and-slash style game, where NPCs say "Please rescue the prince and we'll give you lots of gold", and then you go beat up some monsters, rescue the prince, and receive lots of gold. Implicit in this style is that the ends do justify the means; your characters can be mercenary or rude, or even wreak havoc out of boredom, and it's all taken in stride because you're there to save the world. It's not everyone's cup of tea, but if you come from that to a style where NPCs don't know you're the heroes, have more nuanced personalities and problems, and react accordingly, it can be jarring.
• He feels, out of character, that he's made sacrifices for good causes over the years and people don't respect him or cut him enough slack for it, and is frustrated to perceive that dynamic being replicated within the game.

Specific advice

If the above rings true, I suggest doing the below:

• As GM, modify the game to be more like what your players want, possibly like I've described above: get a quest, achieve it, get the reward. Depending on people's familiarity, this may also be easier for everyone as you're getting into the game. Tynam's answer has some excellent specific techniques for tweaking the game style to meet halfway and helping him achieve his goals without running roughshod over everyone.
• Encourage everyone to make sure their characters reflect the type of game experience they want to have. (I would freely allow people to change or swap out their characters for this reason - this is no time to stubbornly prioritize continuity.) If someone wants to play a socially coarse brawler, let them, while making sure they understand that this will incur certain reactions from NPCs and will require others to take the spotlight during social scenes. If someone wants to play a friendly, gregarious type, make it clear you expect that to be borne out in their dialogue.
• Check in frequently to see how everyone - including you! - feels about the game. If people aren't happy, adjust where possible. If his behavior doesn't change, make sure you've made it clear that this is not only irritating, it's a deal-breaker for the rest of the group.

Outcomes

I see a few possible developments here:

1. You discover that there's a particular style of game your dad likes, everyone else likes it too, and the day is saved. Hooray!
2. Your dad likes one style, everyone else likes another. Suboptimal, but once everyone's aware of this fact, it's usually possible to compromise so everybody gets their favorite thing at least some of the time, and can tolerate the other segments for the sake of continuing the game. If this is the case and he's having fun sometimes, he might mellow out the rest of the time.
3. You can't find a style he likes enough to choose not be miserable to play with, or his idea of fun is honestly totally incompatible with the rest of you.

If it's #3, you have some tough decisions to make. At this point you'll probably have to choose one of the following, depending on how you're balancing the various relationships involved:

1. You all placate him, doing whatever he wants for the sake of continuing the game. I really can't recommend this - "fun" activities where not everyone is actually having fun can sour people on RPGs (not to mention family activities altogether) for years to come. I mention it because it may be suggested, particularly if someone in the group is REALLY prioritizing the relationship.

2. "Look, you don't seem to be having a good time, and the rest of us definitely aren't - I know it's frustrating, but I think the rest of us are going to try doing this the way we want to do it, and we'll find some other way to socialize as a family."

3. Dropping the game entirely. It was a nice idea, and you gave it a shot, but it wasn't working out in practice as either a fun game or a good way to spend time together as a family, so it doesn't make sense to continue. Hopefully a substitute can be found - Netflix, 20 questions, whatever.

If this were just a friend or acquaintance, I'd've likely jumped straight to one of those last two, considering you'd already had a conversation about the specific issue. But you said you really want to try to make this work, so hopefully the above will help with that - and if not, you've still got options.