I want to dual boot ubuntu 16.04.1 and 18.04.1 on my system and want to have a common Home folder for both OS. How do I do so? Will there be any problems? Also which one should I install first?
If you have a separate home partition(say /dev/sda3), you simply have to select it on installation time to mount on /home and not to format. If you have not a separate partition you can do two things,
1: Mount the old installation disk on /ubuntu (not necessarily ubuntu) in new installation. Then link home directory inside it to /home.
ln -sf /ubuntu/home /home
2: Make a separate home partition. Copy all old contents(there in /home/*) to it and mount it to /home in both of installation
here is a simple partition guilde https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/deployment_guide/s1-filesystem-ext4-create
Problem or not? Generally, there would be no problem. It might be a problem if you would like different home configuration. For example if you would like to use "Powerline" on one and not on other. If you would change configuration files like .bashrc in one, the other will get same effects. So you would not enjoy separate home configurations(I don't think this, a problem)