Firstly, you determine the winner of the trick. In this case, it is the last person to play a 5, because in the case of ties for the highest, the last one played is the higher. This player will win all the cards except their own 5.
Not sure how you come to this conclusion from reading the rules. Why should you determine the highest card first? Why shouldn't the first determination be the lowest card? Why can't you look at the rule "the last card played of the lowest number is considered the loser and takes the highest card."? And from that determine that the last 5 played is actually the lowest card?
Can we get a clarification from the designer or game testers?