Well I think the title says it all really..Going to try and post a pic to give you an idea of their size. The smallest one is tiny still
Citrus roots separate very easily. Take your time lightly shaking the dirt off the four of them. Untangle the smallest one first and place it in water then the next size up. Separate the larges two last, working more with the smaller one. This way you can separate all 4 with NO root damage. Get all 4 separated and into water first then replant as citrus do not like there roots in air. I have done a lot of work with citrus from seed. The link below connects you with a how to of mostly pictures with short write ups.
Picture below is a seed grown sweetlee tangerine tree at 10 months age
Click on any picture to open my photobucket display on growing citrus. All pics are open to public so feel free to around for ideas on what works.
Here is a link that might be useful: http://forums.gardenweb.com/forums/load/citrus/msg0320572518736.html