An IP address must not conflict or you will see problems. I generally assign my remote users like this;
Tom= 192.168.1.0/24
Dick= 192.168.2.0/24
Harry= 192.168.3.0/24

A different method would be to assign them a static address at the high end like 192.168.1.24 and keep track of the assignments as you add them from the top down; 192.168.1.23,22,21 etc... This must be balanced with the number of systems your router is assigning through DHCP as they will increase starting from the router=192.168.1.1, then it will dynamically assign 2,3,4 etc...

Tony.