I've worked in dementia care and usually we've only had 4 people when the 4th has been the nurse checking dressings or skin integrity etc, on a resident who needed 2 for manual handling and the 3rd person for clean up etc, but I have known it, for the safety of the person and the care staff. It was while showering and two were either side as a 'buffer' diverting attention away (we used chocolate - his favourite!) while one washed and the other passed soap, shampoo etc so everything could be done as quickly as possible - for the persons sake, it distressed them, but was necessary, and the quicker it was done, the less distress caused. The carers either side were the only ones who spoke, to lessen the overwhelm of several people talking at once, and as pp says we linked arms and were effectively there to take the brunt of the physical response, being pushed against at closed quarters rather than punched full force, so while they were shoving at one carer the other one is offering a chocolate to distract. Someone throwing limbs about also becomes unsteady, so you were also there to support balance and prevent them falling. All this was documented and discussed with family and GP and mental health practitioner, because ultimately it was that, sedation or no personal hygiene administered. It was the least problematic method.
I think you need to know the roles these 4 carers are taking, 4 would potentially be overwhelming and intimidating but may be necessary for everyone's safety.
Unfortunately while as a carer I totally understand that the violence is not the person's fault, that doesn't lessen any resulting injury, nor does it hurt less. I've had my fingers broken from being twisted, more bruising than I could ever count and have scars on my arms where I stood between two residents, one trying to attack the other - this is the reality of dementia, and I still have problems with my fingers now, because of the mechanism of injury. So consideration does need to be made towards the safety of the staff too.