Just sentences

1) I had stopped and then had to catch up with my group. I don't think this is grammatically wrong, but typically in prose you would just use the simple past here for both verbs.  The "then" is sufficient here to let us know that the catching up occurs after you stopped. 
2)When you go to a hotel, you have to check in before (you get a room) or (getting a room).
3)Our family had to check out before 10 am because a new client was going to be checking in. With the imperfect in the second section it sort of reads like your family were rushing to check out while the new client was checking in.
4)If you want, I can drop you off outside your university.
5) I left my telephone in the library, and because of it so I have to get go back.
6)I was very angry and shouted at everyone to go away.
7)No one could keep up with me, because I was running. Don't need the comma.
8)Someone pulls in and waits for another car. Sounds ominous!
9)When my father went to Londonm we saw him off at the airport.
10)We are going to set off for France next weekend.