I just rewatched Back to the Future trilogy..
CHILDHOOD!!!
And,well it's kind of obvious Marty and brother and sister shouldn't even exist.
Once were you mess with your own life before you even born,it will change lots of lives.
Obviously sex,pregnancy and sperm. It would be whole other dates. Therefore,different looking people.
Marty might exist,but sure as hell wouldn't look like Michael J.Fox. And with different character.
There are plenty others stuff as well. Like the hell George and Lorraine didn't figured Marty looks exactly like 'Calvin Klein' in 2nd paradox??