Timeline with Deadline tied to another date column for start and updates

I have a board with projects listed that have an install date. From that install date there are 4 deadline items w/ status that are either 12, 9, or 6 weeks prior to the install date. I want to set the end date for each by setting the install date only. I also want to update these dates when I change the install date. I can do this with formula columns but that is not how I want to handle these. Looking for suggestions.