In this work we compare the ferromagnetic behavior of ultrathin FexNi(1-x) and CoxNi(1-x) films grown on Cu(100) epitaxially with varying stoichiometry. The thickness regime chosen was 1 to 5 ML over a wide range of alloy composition. Using a finite-size scaling law we proposed for the Curie temperature vs. film thickness measurements, we extrapolate and plot the bulk fee Curie temperature as a function of composition. The results suggest that the growth of these films is pseudomorphic with the films adapting a fee structure and the Cu lattice constant. Besides, the Invar effect is not observed in these ultrathin films of FexNi(1-x) alloys and the magnetic phase of Fe atoms is the low-spin ferromagnetic phase. The CoxNi(1-x) films show the expected monotonic decrease in Tc with increasing Ni content.