My Dad's sister found out that she wasn't his cousin but instead his sister via researching the family tree. She was able to go back to the 1600's but passed away before she got further.

I have a copy of where she got upto. We go back to the first fleets. On my ex's side his family goes back to a Great Great Great Grandfather who was transported for plotting high treason...he was to be hanged but got a last minute reprieve and landed here instead.