If your father expresses what he wants for his service then that is what he should get. I guess his estate is paying for it? If not and you are in charge of arranging it you don't have to choose a die hard elder to take it - at least not in the UK. (Unless you want a Kingdom hall service and lots of jw's don't over here they just have a talk in the state owned crematoriums and anyone can give that at the next of kin's instructions.) By next of kin I mean whoever has authority over the dead person's estate and who releases the funds. He who pays the piper calls the tune as the saying goes.
I've known families that were jw's choose a friend of the deceased - sometimes ex elders or reasonable speakers who have never "reached out" and who will be prepared to tear up the "wonderful" jw outline and tell everyone about the dead person's good points.
I did one once after I resigned as an elder - just put in a scripture about the dead persons hope (resurrection of the righteous) and how we could benefit from copying her good points (kind, loved family, looked after grandchildren) and gave her history in what I hoped was a light and kind way. The service was about half hour with a kingdom song chosen by her family and a prayer by her jw nephew but at least 80% of it was about her.
But I asked what the two sons wanted and they just told me loads of anecdotes and stuff which I related. Seemed ok with dubs and non-dubs and most importantly family.