… though you wouldn't think it from the way they acted.
Is there a French analogue of “though you wouldn't think it”?
Here are some idiomatic phrases, but more likely to be heard than to be read.
"en les voyant": looking at them
There is an old French saying which is often used in similar situations (but you can't 'embed' it in a phrase):
Who would have believed this (before seeing the evidence)?
The following should fit when the phrase strengthens the hypothesis it is reffering to. (Have a look at this question on EL&U, luckily it is the case in the context you provided.)
Here “though you wouldn't think it from [X]” is translated as “bien que [X] ne le laissait pas supposer”. Instead of bien que, which is closer to even though, a few alternatives exist:
Within the context you provided, a conditional mood might fit better:
Also, I don't think that “Qui l'eût cru ?”, which is nevertheless a very good idea by Yves, can be used in this context. It suggests strong surprise, related to a revelation backed by evidence.
And, in casual speak, one would probably use the idiomatic phrasing given by Gilles:
But, be aware that without a conjunction like bien que, one could perceive the first sentence as sarcasm.
Légèrement informel, mais je trouve cela bien plus idiomatique que les autres formulations proposées :
On peut utiliser le conditionnel passé (« on ne l'aurait pas dit ») pour marquer que l'apparence est fausse. Le conditionnel présent (« on ne dirait pas ») peut être utilisé que l'apparence soit vraie ou fausse.
« On ne dirait pas » est à peu près équivalent de « you wouldn't think it ». Exemple :
The translation would be better if we had the whole sentence, but the quoted part would probably translate to :
or, more casually :
or, less litterally :
This third version being, in my humble opinion, more euphonious (euphonic ?) and naturally-sounding in french than the first two.
N.B. base anglophone trop faible : pas très sûr du temps du verbe avoir : on doit pouvoir aussi utiliser vous n'auriez pu