Devin is correct. I think the problem here is that you are looking at Wordpress in a different way than we are and thus are not seeing the 'Wordpress way' of doing things.
1) create 3 portfolio categories : Accounting Department, Customer Service Dervice, Sales Department
2) create 2 more portfolio categories : Summer Clothes, Winter Clothes
3) Create 3 Pages (not portfolio items, but Pages). Create John, Sue and Dan who will be the 3 employees. You can leave pages empty for now. Just save them.
4a) Create 3 portfolio items (John, Sue and Dan to match names from step 3) with each portfolio item being the name of an employee and add one portfolio item category to each, so John is in accounting category, Sue in Customer Service and Dan in Sales. , one employee in each of the 3 departments.
4b) Only add the employee image, and link the image to the page from step 3. So John the portfolio-item (step 4a) will be directed to John the Page (step 3)
5) Create a custom template and call it my-employees. Add element portfolio to template. Inside element Portfolio, You will see 5 portfolio categories (step 1 and 2). Only select 3 categories from step 1. Save.
6) Create New Page and call it About or Employees and add the custom template you made in step 5 to it.
Now if you look at your page fro step 6, you will see a portfolio archive with 3 images , but when you click on the image you will be taken to the Pages from step 3 and not to Portfolio Items in step 4.
Do you understand this logic? Please do it and you will see the benefit, because you can now style the individual employee pages by adding one dynamic template to each page for employees. You would do the same process for (step 2) above but only use the 2 categories about winter clothes and summer clothes and ignore the employee categories.
Once you grasp this concept , i think you will have no problems.