Dieting one dog and not the other -tips

[4x4]

I have twin male poodle spaniel crosses who are now 4yrs. One has always been stockier and at 2yrs one was 6kg and the other 8kg. They were neutered and the porky one has gained 4kg and was recently treated for suspected pancreatic problems after bouts of vomiting and diarrhoea.
Usually they share food . A bowl of royal cain biscuits am and a bowl of cooked rice and liver pm. They were eating scraps but I have stopped that .

I have bought special low fat biscuits for
porky and started to separately feed them which is difficult because they are almost magnetic . I have
noticed skinny eats very little and porky obviously took the lion's share.
How can I diet one dog and not the other ? ?

You are going to have to persevere with feeding them seperately. Maybe use a stairgate so they can still see each other.

Good idea about the stairgate. Also, it's never too late to start rewarding with a few minutes play with a special toy, instead of a food reward (if you currently do food rewards).

Thanks stairgate is a fab idea !