Here are the correct verb forms for each of the sentences you provided:
I saw you in the park yesterday. You were sitting on a bench.
They were travelling to Canada when they met each other.
While I was listening to music, my brother was doing his homework.
What were you writing when your computer crashed?
As he was passing the bank, a man in a mask knocked him onto the ground.
Tom arrived while the children were having their bath.
He came while I was having breakfast.
What were you doing at 10 o’clock on Sunday?
What were you doing when the phone rang?
While she was cooking dinner, she cut her finger.