The competition and cooperation between ferroelectric and antiferrodistortive (AFD) instabilities are studied using pressure dependent Raman spectroscopy on polycrystalline powder samples of Sr1-xCaxTiO3(x=0.0, 0.06, 0.25, 0.35). For x=0.0 composition, broad polar mode is detected in the Raman spectra above 6 GPa, while for x=0.06 composition the polar modes appear well above 9 GPa where the AFD modes showed strong suppression. In x=0.25 and 0.35 composition the application of small pressure results in appearance of strong AFD modes suppressing the polar modes. At elevated pressures, re-entrant polar modes are observed along with broad AFD modes and new peaks denoting lowering of local symmetry. The reappearance of polar modes is found to be related with pressure induced symmetry disorder at local level indicating its electronic origin. The re-entrant polar modes observed at higher pressure values are found to be significantly broad and asymmetric in nature signifying development of ferroelectric micro regions/nano domains coexisting AFD. The lower symmetry at local length scale provides a conducive atmosphere for coexisting AFD and FE instabilities.