Maybe check out all the things mentioned here… costs, visas, healthcare ( vitally important…we never think anything is going to happen …until it does) lack of any rise in pension, loss of benefits if needed and no savings, etc etc… and make a list ( spreadsheet.?) of everything… then show him what it will cost.
What is his hobby, can he do it in Portugal… language problems, not everyone speaks English. Ease of getting British things/foods… all such will be more expensive over there.
So if you are the paperwork person…do this and show him the pros and cons both financially and mentally… loss of friends, amenities, grandchildren, etc.
Finally … maybe book a 2/3 month ( whatever is the maximum allowed) holiday rental, where you have to do all the catering etc, for yourself, and go out and find out what it is like actually LIVING there. That might change his mind, particularly if you insist on him helping with all chores etc, and not just sitting on a balcony being waited on!?