whenever second player joins realm, everyone crashes

Word began as a realm. Started having problems when visiting the nether. Super laggy... when playing with two users, one users interactions were very far behind in time, other user was visible but, state was behind their actual actions... but could see the interactions the first user had in real time.

Wolrd file:
https://drive.google.com/open?id=0B7m91QKkuPYnZ0xzckMwX0hmQTA

Downloaded the world file, uploaded to another realm. Works for a single user but as soon as a second user logs in, minecraft crashes.

Earlier, sheep, cows, horses started dissapearing...