Premarital relationship

Q: I am in a relationship with a girl who is my relative since the past 7 months and I really love her a lot and have strong plans of getting married to her. We got physical a few times as in kissing and touching but never in intercourse. I even talked to my parents about this but my father doesn't agree due to relationships going wrong between her families. My question is how do I convince my parents on this and will I be considered as disobedient if I go against them and is there any way I can repent for my sins. I am really confused and I want to get married to her in accordance to Islam and can't think of any alternative.

Focusing one one's duties and obligations

Q: As I am no longer a teenager it is obviously impossible for me to turn back into a teenager even if I make dua for such a thing to happen. From the hadeeth which speaks about the last person to enter jannah, we know that not all Muslims will get to Jannah immediately and some will have to burn in jahannam first. So it is impossible for all Muslims to be saved from jahannam. Therefore what is the point of the ulama asking us to make dua to Allah to save all Muslims from jahannam when it is an impossibility that all Muslims will be safe from jahannam?