>>> fa sret[h] sinni ar sás
>>> we were a following in which he was satisfied.
> I'm a little unclear about the grammar of "ar sás" and how
> to get "with which he was pleased" out of it. Can you lead me
> through that?
Literally "in regards to which he was satidfied".
I took 'ar sás' in line (d) to be parallel to 'ôr fhâs' in line (b).
Preposition 'ó' + relative particle + ro = ór
Preposition 'i' [does not take rel. particle] + ro = ar.
For Mod Ir. 'ar' in this sense see DIL I 70ff.