  In this work, an extension of two-point Ostrowski's formula for $n$-times
differentiable functions is proved. A generalization of Taylor formula is
deduced. An identity of Fink type for this extension is provided. Error
estimates for the considered formulas are also given. Two-point Ostrowski-Gruss
type inequalities are pointed out. An expansion of Guessab--Schmeisser two
points formula for $n$-times differentiable functions via Fink type identity is
established. Generalization of the main result for harmonic sequence of
polynomials is established. Several bounds of the presented results are proved.
