I think the first mistake that was made was your decision to move into his house to make it the new family house. It's amazing how attached we become to our properties and how difficult it is to start 'sharing' it.
It sounds like your OH still sees it as HIS house and that's the trigger of your issues. You didn't want your son to pay his keep because you consider the house as his too. Your partner doesn't, so he saw it that it was right that he should pay something as a lodger would.
Your partner feels that your son is taking advantage by getting the benefits of using HIS house whilst not prepared to give anything back (ie. paying for the occasional take away).
Your son sees it that it's the family house and therefore as a family member, he should be able enjoy its benefits like everyone else.
It's no surprise therefore that he would consider your OH as a control freak, whilst your OH considers him a spoiled brat.
I personally think that the right position would be somewhere in between. Ideally, you should have moved/should move to a 'neutral' home. You should then be on the same page in terms of at which point children who move out become guests/lodgers rather than still residents. There are no rules, very much depends on families.
My view is that when my kids move out, they will stop being 'residents'. They will 'only' come back if they need to, ie. need to save for a deposit, need a temporary place etc... rather than moving back as a resident. As such, I might not ask them for any keep (because we don't need the money and that would allow them to save), but I would make it clear that this was a favour and therefore I too would hope they would do little things in their gift to show appreciation.
As it stands, i think it might be too late to get to that position, so you are best to keep things quiet. Your eldest needs to pick himself up and become independent which you should continue to support him doing, being there for him etc... Hopefully, as he settles in adulthood, he will be able to let the anger go as will your OH and at worse can be civil to each other at family gathering, or at best, rekindle their relationship.