why isn't he happy about you and your son not going to the al-anon meeting? If he wants to go to the aa meeting fair enough.
Of course it is not inappropriate for you to ask, asking isn't a demand. I also get why after all the damage of drinking, with 7 months of sobriety, no job and 4 meetings a day, you would want him to spend 1 evening together as a family on your son's birthday, I personally don't think it's a big ask. but I'm not an alcoholic struggling with sobriety. I also don't get why you shouldn't be able to make the choice to have the evening with your son on his birthday without him being unhappy about it, expectations and resentments go both ways.