Evening Concerneddad
This is the link to the CAA MEP requirements
Multi-engine piston rating (MEP) | Private Pilots | Personal Licences and Training clearly stating a minimum 7 hour theory & written exam at the end.
All flying courses are quoted in minimum hours but it is not uncommon depending upon student, weather and other variables to this to be exceeded, sometimes by some margin. No school should want to exceed hours significantly just for finance as it has the opposite effect on marketing how good they are.
When I did my CPL/IR many years ago I was one of only a dozen or so that completed that year in the minimum time frame. One must budget 10% minimum over run/spend.
Difficult to comment on your son & his training though it does appear a little strange. Either he is useless/dangerous or he has a poor instructor or the instructor/student relationship just isn't working. I suspect somewhere in-between lies the truth. As an ex FI I should only raise my voice or take over if a dangerous situation was getting close. You should just be calm & positive input with aim on praise for things done correctly.
Remember flying is supposed to be fun, it currently isn't and something needs sorting.