Expanded Property Parent relationships. I

My building is a fourplex with four condos: two downstairs and two upstairs. I have created a property that "combines" the two upstairs units into a new, single combined property. Each of those upstairs units lists the combined property as a Parent. I have also combined the two downstairs units into a new property. At that point I will have two "combination properties," one for the upstairs condos and one for the downstairs condos. Next I want to create a top-level combination property that combines ALL the downstairs condos with ALL the upstairs condos. Currently in IGMS a parent property cannot itself have a parent (as in the bottom method of the attached pic.) Also in IGMS, a property can have only one parent. This means that I can’t have a listing that combines all my condos into a single property AND have two properties that combine two condos each.