Unless they fail to deliver as promised you may incur liability for backing out of the deal before occupying. A reletting fee may be the least of...

You are going to need to formally evict them.

Yes your property manager can be your agent in court. No you can not get a writ prior to court.

Either on your own or through your attny work out a settlement with the LL that makes the eviction case go away.

Yes you can but the likelihood of success will depend on whether you gave proper repair notices and were in good standing at the time.

If the case is dismissed you should not be responsible for any costs you didnt incur.

It sounds like there was NOT an agreement to extend the lease so you are not bound.

Subletting depends on a LL allowing it and finding one that fits the circumstances. In this case it seems unlikley that you could be forced to share.

This depends on agreements (writen or oral) that are in place. If there is a notice requirememt then comply with it.

If this is at the end of your lease and they have given proper notice there is likely nothing you can do.