$$$$$$$That's the number one problem why nothing gets done right at my house including the house, number two is the lack of know-how.
Your brother-in-law must think that, one's mans trash is another mans treasure, and it's great to take kids to the dump and bring everything with a motor, that way the kids get to tare it apart and see how thinks work, you know when kids have gotten smarter when they can put the stuff back together with no extra parts.
One of the few things left we can treat wood with is borax. There is a commercial product called Tim-Bor used to treat wood, or you can mix up a solution of good old 20 mule team Boraxo and soak the wood in it.
Do a Google search for "borax wood treatment" or similar and you will find lots of information.
Now, the boron compounds are water soluble, so I would be inclined to treat the wood, let it dry and then cover it with tar paper or metal flashing to protect it from having the borax dissolved out in the rain.
This is cheap and reasonably effective.
Wood Protection and Biocides
This is an interesting read but no mention of formulation or mix ratio.
I bought the useless treated 2x4s to make a gas can locker outside. I was planning on using the 2x4s to lift the "box" off the ground and for framing.
If anyone finds a mix formula for applying the Borax, please post.