There is a statement:
A group may have two distinct characteristic Sylow-$p$-subgroups.
I think it is not necessarily true because if there is unique Sylow-$p$-subgroups, it is characteristic; if the group is characteristic, it is unique Sylow-$p$-subgroup.
Can anyone give some details about this?
The Sylow p-subgroups of $G$ are all conjugate. So if there are > 1 such subgroups, conjugation by some element of $G$ sends one Sylow p-subgroup to another. Conjugation by a fixed element of $G$ is an automorphism.