1 referee, 4 linesman. Easy.
If both Linesman press a buzzer (as so that they can't be influenced by each other) then it's offside, a penalty or a goal. Each linesman gets a quarter of the pitch along with the referee to decide upon standard fouls.
if you need both to press, it would be a disaster. 1 linesman gets say 50% of decisions wrong, say the other one does to. In a perfect world it would be the same decisions and the call would be given(right or wrong) in the worst case neither linesman will agree on a single call. Basically that would never work.
The fact is this, and very simple, we have the technology, it can get any decision right, linesmen and referee's will never in a million years be able to get every last decision right. Its really that simple, how long will the arguments and discussions between 3 linesmen and a ref take when a decision is not quite obvious, I'll tell you, same amount of time, if not less than it would take the same 3 looking at a replay to come up with the right answer.
Video replay is just that, everything else, you can misread things, not see the whole picture so any thinking back to what happened can't be accurate, while looking at video from several angles, which will take 30 seconds, is. WHy go half hearted when it would arguably cost more money to implement? 2 new 60k a year wages, plus security, you just couldn't have a linesman who barely moves standing what at many grounds will be arms reach away from the crowd.
Its just beyond a ridiculous idea. yes a decade, or more like 3 decades ago it would be a possible improvement, but now its just a freaking joke. Even league 2 clubs are all recorded from multiple camera's every single game already, a tv for the 4th official and the ref to look at for 30seconds is just going to be so ridiculously easy to set up I can't see how they can justify adding more people who can still clearly get things wrong to the mix at a large cost. Lets see, every week its a minimum of 2 extra linesmen per game, but you need probably an extra backup aswell incase of injury's, then you aren't allowed to officiate the clubs you support etc, so another round of officials as more backup, instead of using existing equipment and existing footage that is already being shot?