Officially, Pat Anderson is Terri's parents' lawyer. Felos is, or was, officially her lawyer; that's the only way his payment from Terri's trust fund could be justified. Officially, it is in Terri's best interest to be fatally dehydrated, so Felos is working supposedly in Terri's interest.
One of the big problems in this case is that Greer's refusal to appoint a guardian ad litem as required by law means that there is nobody who really has standing to speak on Terri's behalf against her HINO. To my mind, the fact that Felos functions openly as Michael's lawyer while also claiming to act on behalf of Terri should raise some red flags, since it would mean that he could not possibly be counted upon to act in Terri's interests in the event such interests differed from HINO's. But of course since Greer's declared there's no possible conflict of interest, that's a non-factor.
Felos' book, on the other hand, would seem like that would be a separate conflict-of-interest angle which AFAIK has not been addressed by any courts yet.