Does the fact that adultery is not consummated except through penetration mean that masturbation for another is permissible, even if it is with a forbidden degree of kinship (mahram)? And is masturbation not considered a sin unless it is done by hand?

The fatwa you encountered might be related to the definition of zina (unlawful sexual intercourse) that necessitates a prescribed punishment (hadd), which requires penetration. If you are asking whether this implies the permissibility of satisfying one's sexual desires through masturbation by others without accountability, the answer is that the fatwa has no relation to this, nor does it negate the sinfulness of such an act without penetration. Masturbation through others is not permissible except with one's wife or a female slave (malakat yamin). Anyone who exceeds this is sinful, as Allah Almighty says: "And those who guard their private parts Except from their wives or those their right hands possess, for indeed, they will not be blamed But whoever seeks beyond that, then those are the transgressors." Prohibited masturbation includes every means other than one's wife or a female slave.