2 separate points here (2sp-s perhaps?), me thinks.
As to father-son- work at home, think that you need to get your OH at some point and when things are calm and quietly lay your cards down as to needing both of them at home from time to time for the fridge list and that they should be spending some more time together - which could be visiting Grandad together and tackling jobs at home together too, the reward perhaps some pub time or a footie match or whatever they enjoy together..... the issue is for your OH to resolve this with your son, but as long as the jobs get done, you will be more relaxed about the whole thing.
Point 2. Your son should be paying you a contribution and I would also be pointing out that £40 is nothing - outside laundry and dry-cleaning would cost him probably £25 a week minimum, food, tricity and all the rest, inc the TV licence (there's £2 a week straight out). Just point him to some of the reactions on here and that you're happy with the sum as you want to indirectly contribute on an ongoing basis to his savings towards a deposit somewhere down the line.