In order to fix some columns on the left, can you create those three methods on "TableColumnBase" :

public final BooleanProperty impl_fixedProperty();
public final boolean impl_isFixed();
public final void impl_setFixed(boolean);


It means that the specified columns will be fixed on the left, aka always visible.
Like I said, the way I see it, the first "X" columns can be fixed. So I would make those methods protected, and implement a method in the control in order to add that constraints.

But if you want to be able to fix the fifth column without fixing the first four (for example). Then those methods can stay public, but maybe more complex to develop.