Hello! First time posting, long time user

I have a staffing document with all employees in my company. Column titles include name of employee, manager of employee, location of office, etc.

What I want to do is assign a number 1,2,3 to each employee in order to distribute training to them. This I know how to do. What I need help with is ensuring that the numbers are equally distributed within each sales team. For example there are 8 employees assigned to sales manager A - we do not want all of his employees off the sales floor and in training at the same time so I want three employees assigned a number 1, three employees assigned a number 2 and two employees assigned a number 3. It will not always be exactly equal but I want it to be close. Keep in mind employees leave and join the company constantly so the count will fluctuate from time to time (one of the columns has term date in it).

Please let me know if you can figure out a way to evenly distribute these groups!
Thank you!