Ac susceptibility and static magnetization measurements were performed in the
nearly-optimally doped LaFeAsO0.9F0.1 and CeFeAsO0.92F0.08
superconductors, complementing earlier results on SmFeAsO0.8F0.2
[Phys. Rev. {\bf B 83}, 174514 (2011)]. The magnetic field -- temperature phase
diagram of the mixed superconducting state is drawn for the three materials,
displaying a sizeable reduction of the liquid phase upon increasing Tc in
the range of applied fields (H≤5 T). This result indicates that
SmFeAsO0.8F0.2 is the most interesting compound among the
investigated ones in view of possible applications. The field-dependence of the
intra-grain depinning energy U0 exhibits a common trend for all the
samples with a typical crossover field value (2500 Oe ≲Hcr≲5000 Oe) separating regions where single and collective depinning processes
are at work. Analysis of the data in terms of a simple two-fluid picture for
slightly anisotropic materials allows to estimate the zero-temperature
penetration depth λab(0) and the anisotropy parameter γ for
the three materials. Finally, a sizeable suppression of the superfluid density
is deduced in a s± two-gap scenario