In this study, thermal expansion and magnetostriction of members of a homologous series of compounds based on the alloy series Pr[Subscript (n+2)(n+l)]Ni[Subscript n(n-l)+2]Si[Subscript n(n+l) has been investigated to study the magnetic phase transitions. In order to identify the location of magnetic phase transitions for polycrystalline samples of Pr5Ni2Si3 and Pr15Si10, theoretical calculations based on Debye-Gruneisen model were used to separate the phonon and magnetic contributions to thermal expansion from experimental results on these materials. The results indicate two magnetic transitions in each compound, one corresponding to the Curie temperature and the other at a lower temperature exhibiting characteristics of a spin reorientation transition. From the thermal expansion measurements of Pr5Ni2Si3 single crystal, a temperature dependent anisotropy in thermal expansion was observed in the temperature range below the Curie temperature. This is due to the negative and positive magnetic contributions to the thermal expansion along the directions parallel and perpendicular to the c axis respectively. In addition, the characteristics of a spin reorientation transition appeared only in the results measured perpendicular to c axis. Based on the experimental results, the expected variation of magnetization with temperature in Pr5Ni2Si3 single crystal was calculated using a nearest neighbor exchange interaction approximation. The results are in good agreement with experimental observations given the simplified nature of the assumptions.