Did Marty2 travel Back to the Future into a giant plot hole?

Please help me to figure this out. Born into a dysfunctional family, Marty1 alters his parents 1955 timeline. In this new, functional family timeline, Marty2 is born and raised until he disappears in his timeline's Delorean. Dysfunctional family timeline's Marty1 accomplished his mission and returned to Marty2's timeline, which left Marty2 nothing to alter in 1955, and as far as I can tell, Marty2 isn't represented in the rest of the trilogy. Did the film series leave a gaping plot hole, or am I just confused??