Help me find a long lost trilogy!

Hey all, I am trying to find a fantasy trilogy that I had read quite a while ago; I really liked it back then but it was not mine, borrowed it from a friend to read and for the life of me cannot recall the titles or the author's name. Here is all I can remember (sort of):

• It is a trilogy
• I read it roughly between 2005 and 2010, so definitely not new.
• There are more than one protagonists (teenagers/children, two boys and a girl maybe?)
• There are moving cities, but definitely not Mortal Engines
• The protagonists' people want to get to a promised land (across a mountain pass eventually)
• There is a scene where one of the protagonists participates in a gladiator-style fight in an arena but they have blades attached to their elbows and knees.

I know it is not much to go on, but any guess is appreciated.

Thank you in advance for any ideas!