What's the fastest way to rebuild different sets that have been brought together My mom did something to my LEGO. When I was a kid I loved playing with them. Frankly I have no interest in it anymore.  She broke down all them sets, and put them all in a huge box.

I still can figure out some parts, but I don't know if it's better to break down every piece and rebuild from scratch.  I'm not talking about 3 or 4 sets, more like 20 to 30 LEGO sets worth around 3k to 4k euro...  I want to resell it, sadly she took away the building books and the boxes and did them away too.
In order to gain value out of this, you're going to have to put some work in.

Start with the largest sized kit that you remember doing and assemble the parts (find the building instructions online).  Then move onto the next smallest, and so on.

Obviously, you're not going to remember the details of all the kits you had, but the largest ones should be more memorable (and usually they're worth more).