Answer to "Is there any way to change this from German to English?"Um, the family member appears to have purchased it in German intentionally. I studied it for three years in high school and three semesters in college, yet I can barely remember how to say 'hello' these days. German is an excellent second or third language to learn with your children, for it's basically English without all of the exceptions in its syntax, spelling, and sound;) If you are anxious to learn what the lesson recordings mean, simply put the speaker up to your microphone (computer or smart phone) in a Google Translate window however. Hope that helps!
Answer to "Display flex Cable is corroded in search of replacement"Sounds like you need to replace the flex cable, no? https://www.ebay.com/i/132408057873?chn=...
Answer to "any differences between the SSD discs on 13" and 15"?"That's a great idea, but what is the answer to the OP's question? I'm pretty sure they're not interchangeable but hopefully somebody knows the odd balls which can be swapped..