Parent Date Roll Up

I currently have a sheet where  i have multiple columns with dates thats that are going to need to roll up to the project level parent. I am looking for a way to roll the dates without using the predcessor function as it doesnt quite work right. In the picture below you can see some of the columns. I would like to have the dates for Committed roll up. The following columns would have the same function, but not specifically tied to the previous column. 

This may not be capably, but its worth a shot.