In reading the appeal arguments, I got the impression the WT lawyers were trying to play off like the elders have nothing to do with field service (or a least very little). Funny Org itself refers to field service groups as an extension of the congregation arrangement. So what goes on there is there responsibility.
If a single brother and sister were working alone together you bet the elders would get involved in those arrangements and quick, yet nothing was said to any family there about a paedophile who was known to the elder body. I defiantly think they failed to warn.
Ultimately though I would wager WTS will win this, based on lack of evidence and lack of knowledge (by the judges on how things really work inside the org).