Lego Ideas

I want to have a huge lego building event at my church where teams of students work together to transform our youth room into a habitable lego dwelling, at least for a few days. I have many students with piles of legos from their younger days, so getting the blocks isn’t a problem.

Here is where I need some help. How do I get all of the blocks back to the rightful owners? I need a simple, fast way to identify all of the blocks, who they belong to, and an efficient way of getting them back to their owner. I have pondered this for a couple of days and my best solution so far is just to sell all of the blocks at a yard sell and divide the money according to percents of blocks placed in the pile.

Any better suggestions than that?

UPDATE: I never did figure out a good way to seperate the blocks so I just got one guy with an abundance of bricks to bring them. Then we just did an activity with those blocks. The activity was to build some sort of a protective structure and then I think we talked about the protection of God or something similar.