What will work in this scenario depends a few different factors. The following questions are driven by my being a consumer of Speculative Fiction and time-travel work for more than 2 decades.
First, what is your understanding of how time is structured in these movies? There are multiple theories of the time stream. Back to the Future clearly shows diverging but simultaneous timelines in existence. The dialogue around this idea is scant, but it is presented. How are you going to handle the brief dip into this specific theory of the time stream?
Second, how or even will you handle the impact of anomalies created by these two characters crossing and re-crossing their own timelines? The fading picture again shows but doesn't really tell the theory on this course. Is there a "Time Cop"/"Dr. Who" situation with things that cannot be touched or changed?
Third, is there a way for Marty to be conceived before the death of his father OR a different reason that his father is now threatened but would allow Marty to still be alive?
Yes, more questions than answers and these are the questions I would be asking if watching the movie. Most important, in my opinion, is to follow the rules regarding time of the franchise and your manuscript. One of the reasons authors loose readers is when they don't follow the rules that have been built into the alternate world of the story. "We" notice and are more likely to either stop being involved in the story, or give bad reviews when it happens.
Good luck with your project!