Many children have no idea what their mother,s maiden name is. This is why it is important to search as many records on all the siblings you can. I have helped people who have been looking for yrs for the wrong name of their female, just because someone put the wrong last name, on their record. It can be a pain looking for the wrong last name for yrs.
These are some of the places I look for death info. You can also look for info in each county by just putting the county and state in google. Good luck.