How is Damian and dick Wayne related? Biologically/blood relations

Google wasn't being helpful so I just wanna know if Damian and dick Wayne, aka Nightwing are actually half brothers or smth?

Do they share the same mother cause I couldn't find any info on Nightwing mother and how batman met the woman who would later give birth to his son's.

Does anyone know what other franchise shows feature stories of where his son's popped up?