...

type

    TBBase = class
    private
        _a: Integer;
    public
        procedure SetA(value: Integer);
    end;

    TABase = class
    private
        _b: TBBase;
    public
        constructor Create(b: TBBase);
        procedure SetA(value: Integer);
    end;

    TB = class(TBBase)
    private
        _b: Integer;
    public
        procedure SetB(value: Integer);
    end;

    TA = class(TABase)
    private
        _b: TB;
    public
        constructor Create(b: TB);
        procedure SetB(value: Integer);
    end;

...

implementation

procedure TBBase.SetA(value: Integer);
begin
    _a := value;
end;

constructor TABase.Create(b: TBBase);
begin
    _b := b;
end;

procedure TABase.SetA(value: Integer);
begin
    _b.SetA(value);
end;

procedure TB.SetB(value: Integer);
begin
    _b := value;
end;

constructor TA.Create(b: TB);
begin
    _b := b;
end;

procedure TA.SetB(value: Integer);
begin
    _b.SetB(value);
end;

...