Have name changed for this, as I mention security details at my dad's place, just in case anyone anyone "knew" me from my normal posting name. Am a long term MNer.
This will be long as I will try to put in as much back story as possible. My brother and I are in our late 40s/early 50s. My dad is a fit and healthy 75. My mother, to whom my brother was close (as was I) died earlier this year. She had had a long and happy marriage to my dad - but because she had been ill for a number of years (and we were actually wanting her to die for many reasons - not least the fact that she was absolutely miserable as a result of her illness), my dad is the one who has probably "coped" the best out of all of us.
Db has always had issues with his temper but normally this manifested more towards me. He also has a issue with me because I don't see enough of him and don't put enough of an effort into being friends with his wife. As a result, he thinks we are a dysfunctional family. Dh and I wonder if he has an idealised view of how families "should" operate, partly because all of our extended family are in other countries, so there was only ever our nuclear family unit in this country.
Dh thinks if anything, the dysfunctionality is in how often we meet as a family: there is a long standing tradition of going to my parents' place for a Sunday night dinner every week. Db still goes every week, but my family (as in dh, ds and me) now only go once a fortnight. Tbh, one of the reasons we reduced the number of times we went was 'cos db can be very difficult at times (pontificates, is always right) so we reduced how often we exposed ourselves to it. We love seeing my dad though - both my parents were great company and my dad has taken over my mother's mantle of cooking great meals.
When I was younger, we went through a stage of always being on tenterhooks as to whether my dad and db were going to argue. My mum had a way of managing to smooth over the water - but there were many times when I and his girlfriend or wife at the time would escape to the kitchen while he vented.
I need to add that db can be charming and has a lot of lovely friends (although even some of them would acknowledge he has issues).
He is now married to a very nice girl and they have 2 very young children.
There was a blow up at dinner on Sunday night over nothing - but mostly directed at me. My dad had a heated discussion with him in the kitchen telling he need to address his anger issues (normally dad tried to avoid confrontation) and at one point told him to look into the mirror and see his face as the expression on it was venomous. Db wants me to have lunch with him "to save the family" 
- but I've still decide if I want to as he's mistaking me for someone who gives a damn . not least because I'm actually scared of his anger. If I do have lunch with him, it'll be in a public place and even possibly with a friend placed strategically in the same place to rescue me if at some point I get too distressed.
However, that is not directly why I am writing this extended post. My dad had dinner with db last night (which he does most Tuesdays). He is going away tonight for 5 or 6 weeks to visit family and friends abroad. He told db that he was happy for him to use his place (much bigger than the flat that db lives in, with a lovely garden for the kids to play in).
He asked him not to switch the alarm on as it is not working properly and often goes off in the "other" hallway (big old house sub-divided into flats - although my parents' place has its own entrance). Db flipped at this and (apparently - all this is from my dad's description) started berating my dad, saying that he would switch it on and if dad disabled it some other way then he's put in another alarm system. It all got a bit unpleasant.
As dad was leaving and getting into the (small) lift, SIL was trying to apologise to him for db. Dad was telling her that he does listen to db's advice but that he doesn't always have to take it. Db heard this and then got into the lift with dad and started berating him again and saying if he didn't put an alarm in, he's have to visit the house every day to check that it was OK. He was physically intimidating my dad in the small lift and dad told him that he considered what he was doing was mental abuse, although he didn't add that he was (and he was) actually also scared that db's anger could also turn physical.
At this point, db said that he would never see dad again and that he would ensure that he never saw the grandchildren again.
Dad rang me this morning obviously quite distressed. He's always said (because he has been advised by his own friends and family) that he would not get directly involved with the issues between db and me (although db thinks he should). But now he's ringing me asking for advice as to what to do.
He doesn't want to leave on the plane with a heavy heart :(
My dad is coming over later. What do I say to him?