David Banning was known as David Martin, Jr. at birth. But he never had a child with Brooke Hamilton.
Julie had David to David Martin, Sr., but put him up for adoption. He was adopted by Scott Banning and his wife, Janet (who died) and named Bradley Banning.
Julie then somehow figured out that Bradley Banning was her son. She got involved with Scott Banning and married him, becoming David's legal mother. At some point, his name was changed from Bradley to David.
I don't remember David changing his name to David Grant (or even using that name) when he lived with the Grants.
David got involved with Trish Clayton and they had Scotty Banning (named after David's adoptive father, Scott).
Valerie Grant returned to Salem in 2016 (after leaving in 1982). In 2017 when David Banning died, we found out he and Valerie had reconnected after leaving Salem and she had his son, Eli, but never told David. She also never told Eli that David was his father, either. He believed Valerie's boyfriend Terrence was his father (Eli was young when Terrence died). When Eli went to Quantico, they wanted background information on him, so he did a DNA ancestry test and discovered he was not 100% black, then used FBI resources to figure out who his biological father was.