Some considerations which complicate the process, are providing an income for several generations whilst wanting to provide an inheritance to off-farm children. 

So what about the off-farm children?

Generally, there's an understanding that the on-farm sibling gets the farm, the off-farm children at some point begin to wonder where they fit in.  This, in many ways, is where it gets complicated. 

Tony Catt explains this process in more detail answers who, what and how!?