Trouble with LAN server in minecraft?

Whenever I try to host a LAN world for my friends and I, they are never able to connect. I have tried disabling all of our firewalls but that seems to have done nothing. If it matters I'm using an Asus while both of my friends use Macs and every time I open a server to LAN I'm given a 4 number port instead of the normal 5 number port. Any insight on how I can fix this problem would be greatly appreciated.

CAN I SEND MY FRIEND TO JAIL FOR STEALING MY MINECRAFT BREAD?

I play Minecraft on a server with my friends and I have a café in the main town were I sell BREAD, cookies, cake, pies, and soups. I got home from school to find my BREAD GONE! They must have done it when I was asleep last night since we all go the the same high school. I plan on having a full investigation and bringing this BREAD THIEF to settle this in our Minecraft court but I want then to really pay for their crimes.

What can be happening with my Minecraft server?

It keeps getting hung up every once and a while even though it has 6gb of ram dedicated to it and it's a 3ghz 4 core 4 thread with 200mbit up and down connected with ethernet. What can be happening with my Minecraft server

How can I keep a fixed public IP in Amazon EC2?

I'm hosting a Minecraft server on an Amazon EC2 instance.

Every time I reboot the instance, it has a new public and private IP.

How can I keep the same public IP? Private IP doesn't concern me.