I understand that cooking is something virtually everyone does in our daily lives, normally safely - brazing, not so much!
However the concern the OP has is a risk based one, whilst a smaller number can do it safely, she is clearly at a point where there are going to be too many pupils in close proximity, using the same equipment, plus she has 4 identified behaviour pupils and SEN in the mix.
Every factor increases the likelihood of an accident, if it were 2 children per 4 burner hob, each with their own side and clear work area its much safer.
And be of no misapprehension, if it all goes tits up and a kid ends up in A&E with burns, suddenly it will magically be all Ops idea and the HOD won't know anything about it!
CLEAPPS have some diagrams of safe working positions in food tech rooms, worth seeing if you can find those OP.
If you are not familiar with CLEAPPS visit the science technician, they tend to use them a lot more than we do in DT and will be able to access your schools member account to access all the info and contacts.