Although to you there is no reason for this drinking, obviously there is a reason. It could be stress at work, it could be that he feels his face doesn't fit (hence the comments) either at work or in some social sense (is he a member of a club of any kind and has been ostracised - cut out - of this?) - clearly something has happened in his life even if he doesn't share this with you. He may not even have shared it with your mother.
You need to sit your mother down and ask her to explain your father's behaviour. She may try to defend you by saying she has no idea. You have to gently and not aggressively insist (people clam up if you get aggressive).
You also need to speak to these other family members. As they are being nice, it may be that they know something you don't, and are trying to be "understanding" towards your father under the circmstances (whatever they are).
As I say there is clearly a reason for this behaviour and if you get to understand it, it might be easier to tolerate. You need to know if this is going on permanently or temporarily. Tell your mother/family that you are frightened by this sudden change, and that you need an explanation. Saying you are frightened (rather than angry etc) is often the trigger for people to feel protective and compassionate and they may reveal more that way. Perhaps it is that your father is having some kind of breakdown. Does he have a very stressful job? Has he lost his job? Is he going to lose his job? Your parents may not want to worry you with this information so you need to coax it out of them.