I think you would like to do an action after checking the percentage. I would suggest you create a validation sub microflow in that action, which retrieve, maybe on base of a xpath logic to improve the performance, the related properties and built the logic to check the percentage of ownership of the property.
A domain model like this could work for your business case. The PropertyOwnership entity serves as a middle table to show what percentage of each the property is owned by each company. Your vision of a dynamic page can be achieved by putting a list view in your Property data view that retrieves the list of PropertyOwnership over the association. You will need to create logic that checks if the Property has 100% ownership. If not, create a new object of PropertyOwnership, associate to the Property, and refresh the object in the client.
I would show the total percentage on the page. In red for instance when it's not equal to 100 en in green when it adds up to 100. This makes it easy for the user to see if he can submit his input.