ABC here, i understand where you are coming from with a family business as well but not as extreme as you made it out to be. i don't see a problem with this from the father's side. you are still getting money at the end of the day, it's just less until the 70k is paid back right? the real question is why he decided to change it to 250k after providing the 320k. did an argument occur?/something happen in the family? my assumption is your father is testing you/'taming' you by withholding money. is your financial situation where that 3k is absolutely necessary to live or is your wife just being picky?
i think your wife is a bit too demanding but given she's from the one child era, it may have influenced her upbringing to think/behave a certain way. does she work? did she enter the marriage under the assumption she wouldn't have to work? just be honest with her about the 70k being paid out of the dividend.
perhaps bring her into the company? though that could cause problems as well.
given your personality, at this point you should monitor when the 70k is fully paid back and if he is still deducting it, you can probably assume he either forgot or he is trying to weed off your dependence on these monthly 'dividends' and for you to maybe survive/provide for your family with your own salary until you take over?
perhaps just casually ask him one day (calculate first how much he withheld the dividend) the remainder of the amount you owe him and that you will write the check out to him on the spot then see from there what the real deal is.