Question

increase number of ancestors

Answer 1

set 50 Parents, 50 children, and 50 others and more ancestors will show up

Answer 2

Maybe your "question" will be solved by the following.
 

Try this:  

Click Options  In the fifth column You will see Parents, Children and Others.
Set all three to 50, to see the effect. No "disappearing" family anymore!

In reality you probably want these values to be lower than 50, especially when your tree grows large:
Because e.g. lines between couples can get very long otherwise.

Good luck!