Wife Nettie SALYER Birth:29 MAR 1888, Morgan, Kentucky (could be a typo for 1858) Marriage:1875, Magoffin, Kentucky
Ok, being as you don't have anything solid to go on, I would get Robert's birth cert. You have a year and a place and he is married to a Nettie Slayer. They automatically search two years both sides. You may be able to get the cert for half price as they don't actually have to do a search. You need to check as this may have changed but worth it.
His birth cert should have his parents details and marriage date and place on it. You need something to go on. He may be the eldest but if not it should list anyone born before him.
This will give you the solid info you need for Samuel and Lizza. Sounds like she was known by Elizabeth. Her mother could have been Hannah.