Sorry to hear your sad tale ,,,one of the reasons I am glad that here in France inheritance law is very specific ....everything to the children (inlcuding the inheritance tax, funeral costs and payment of any outstanding commitments !) ...you can take out life insurance to ensure they do not have enormous bills to pay prior to them selling the house (or living in it if they want)...and if you have step children as we do, the Testament can state that on the death of the first spouse, everything is left to the surviving spouse, with proviso that on the death of that spouse, the property is split in equal parts to the step children. If this is not specified, then, for instancem if the husband died first everything could go to his child, and you may or may not be granted a right to live in the house under usufruct ..although there is also a requirement if the child sells the marital home some provision for the surviving spouse must be made. No one can leave a house to the Cat's home (although we would like to !)......the children can also declare they do not want to take up their inheritance, as often it will involve enormous cost ...and they must then make a notorised declaration to this effect !
In my case, when my mum died, my dad inherited the house, sold it and bought a retirement flat (we were very happy for him to do so ) ...and then left the money from the sale of that, plus some small investments, to my brother and I in equal parts and he also had a funeral plan ...brilliant ! I HATE those funeral plan ads on tv BUT they really DO make sense. All we had to find was the money for the redecoration of the apartment, and solicitors charges (which were covered anyway by the inheritance ,,and as it was only small, there was no inheritance tax !
It does sound in this case however that the son (he is after all 40 years old !) had an expectation beyond what he received ...which, given that you say he lived rent free in your holiday home to write (what luxury !) I guess he should be asked for retrospective rent money ...seems he has already been give more than enough !..other than that I would ignore the request ..BUT be prepared if he should contest the Will, and have all bills relating to loans, rent free accommodation, other things paid for, etc etc as the only way you can prove he had been sufficiently helped over the years is a paper trail.....
You really do not need this at such a time ....but you do have your children for support ! bon courage 