And you judge that inquisitor was suprised by Teagan arguments by exactly what because i didn't saw shock on inquisitor face nor any indicator that inquisitor didn't know about that when Teagan presented Ferelden position.Also during main game you were still dealing with Corypheus.
In fact it was fairly obvious that Ferelden doesn't want Inquisition in its borders as i said council was delayed for 2 years in favor of inquisition by divine Victoria and Ferelden and Teagan doesn't hide their position.
1st-For his/her response on Crestwood being occupied by bandits before the Inquisition kicked them out of the town.
2nd- I don't know which point you want to reach with Corypheus still screwing around, if it's about the territories the Inquisition had, Ferelden may disagree since then and may ignore it to avoid problems and still get aid from the Inquisition, but if they weren't happy with the Inquisition on town, then they should not offered them a way to have even more lands.
3rd-No, they don't hide their position because the Inquisition is no longer useful to them, it seems that backstab whoever aided you once it stops being useful it's something very Fereldan.