We test the influence of two thermodynamic effects on the dynamics of equiaxed Al-Cu dendrites growth and interactions in thin samples. The first effect results from the nonlinearity of the phase diagram with the copper concentration and the second effect is due to temperature fluctuations. The study relies on three-dimensional phase-field simulations of isothermal solidification in confined samples, for which thickness is of the order of the characteristic diffusion length. We compare the present results with those of a previous study that did not take these thermodynamic effects into account [A. K. Boukellal et al, Materialia 1, (2018)]. We show that including these effects does not affect the scaling laws derived previously. This result strengthens the conclusions already drawn and encourages the application of these scaling laws to predict the behaviour of dendrite tips in more physical situations.