These immediately presented a couple of problems.
Because some of the drawer's parts were sagging, these would catch the contents of the drawer below. So this results the difficulty of opening or closing BOTH drawers.
Also, with some of the drawer's plywood parts jutting out, the drawer became unsafe to use. It's either the rough plywood or the small nails that would scratch the person using it.
I emptied the contents and pulled out the drawer. I intended to fixed the drawer and so I closely inspected how it's built.
After putting to memory its basic structure and how all the parts are joined, I disassembled the drawer as shown below. Note I only dismantled the parts that were falling apart already. If there are parts that were breaking but still attached, you could use a spatula or dull knife to pry them apart.
Now here's the messy part. With a white glue or craft glue that's suitable for wood (I used Stikwel), slather on all the parts of the wood that will meet when joined.
Ensure that even loose parts that were not dismantled get liberal slathering of the glue.
Join them all together and ensure the joints are correct and snug otherwise you may not be able to slide the drawer back in!
You might want to add new nails on joints that had rusty or loose nails.
Here's a nifty tip to keep the glued parts together - CLOTHES PINS! They're like little clamps that will keep the glued parts until dry.
Put clothes pins wherever applicable and then let dry.