The bulk impedance parameters of polycrystalline samples of the Pb1-x-yInx-yBi2yF2+x+y (fixed x, 0 less-than-or-equal-to y less-than-or-equal-to x) solid solution with fluorite-type structure were determined from an analysis of ac conductivity data measured in a wide temperature range. Hopping rates of mobile F- ions were extracted from frequency dependences of conductivity at different temperatures. The concentration of charge carriers in the samples investigated has been estimated. Independently of y, its value (log N/cm3, = 21.6 +/- 0.02) allows to propose, on the basis of the clustering model, that charge carriers in these materials are likely the interstitial fluoride ions of F" type.