Our neighbor died years ago, and we asked her brother about selling the home to us, but he said no. We live in Richmond, California and would like to fix up the house and backyard for ourselves, any help or suggestions?

It isn't abandoned as long as someone is paying the property taxes, so go to the tax collector's office and find out. They or the deed office has the owner of record on file (assuming that the heir or heirs are now on it, as they ordinarily would be by now). Any liens for other debts will be there too.
If the taxes get far enough behind, the city will put it up for auction. You can bid on it then.
If you don't like the condition of the house and yard, complain to zoning or whoever handles such things.
You could try to approach the heir again. Their address should also be in the tax and or deed office.
Fixing up the place won't get you any rights, and could even get your arrested for trespassing.