iphone 6 plus stolen

Few days ago my phone was snatched from me and the thief forced me to tell him the keypad lock, i reported the case to local police and gave them IMEI# of my phone. The case is still in progress.

Further findmyiphone service and application both were enabled in my phone and i put my phone on lost mode. After 3 hours of theft i got an email that my phone is found at a location where hundred of mobile shops are present that deal in second hand mobiles, where it is impossible to search for mobile. Simultaneously, i got password reset email and a notification that the location services of phone are disabled and it can't be located anymore. I changed the password and again put my phone on lost mode but since then my phone is offline.

I need to know is it possible that i turn on the location services remotely on my phone or are they automatically enabled when the phone is put on lost mode?

Is there any way that thief breaks my icloud's password and resets my phone?

What if thief deletes findmyiphone application? will he also able to disable it's service from settings? what will happen then?

is there any possibility that thief can change the IMEI# of the phone?