How easy would this be to code?

I want to create a family tree program with a difference. I want user to enter their name, parents names, number of brothers and sisters and their names. And maybe place of birth and DOB.
I then want others to be able to input their data.

Then when a user enters his name into the get results screen. I want program to draw up a tree of relationships and show cousins, parents, siblings, grandparents etc.

I know that you have to create MySQL tables - but not sure how many I need to create.

Also how do you create GUI in php?

I know how to connect to the database and create a database.