SEP IRA contribution among control group

Hello,
Thank you for your help in advance. If a business owner has three entities to be included as a control group, does the contribution have to come from each entity based on the w2 the owner is taking from each entity? or are those 3 companies treated as one entity?
For example, would it be possible to increase his w2 from one entity to the point where he has no K-1 and fund it from the profits from the other two? we are trying to see if we can increase his wage from the company that has more employees.

I sincerely appreciate your help. Thank you.