The reason for the choice of Gweyr if they give it to you but not explicitly, as much as it seems that Gweyr and his daughter Gwyn do not look alike, that is not so in a very important aspect, respect for her father. Gwyn says that her father was a person who could not bear nonsense, she followed the advice he gave her and that kept her alive throughout her life while she watched as the newbies who joined them died. As much as they were the children of neighbors, she would not give a chance because although the whole village would hate her, it would be more difficult to take care of her children if she was murdered, I lost against the boss who I do not remember his name, he was about to kill you if it were not because Sanders helps you.
Gwyn followed Sanders '"right choice" for a while ignoring the experiences that had kept her alive exactly for the sake of her children, perhaps for months, and both Sanders and the boys' parents had tried to convince them and failed, And now they had kidnapped a girl, to all the groups she encountered she gave one last chance that surely in her days as a mercenary she had not even thought of giving them, except for those of the statue, since River's life was at stake, Gweyr did not let the innocent newcomer suffer the consequences of not acting sooner.
Given Sanders' seeming ineptitude, the baroness's obvious indifference, and the lack of reasoning of her enemies, Gweyr made the judgment she believed was correct. Most likely, if Sanders didn't exile her, the other half of the village would have supported her and the only culprit would have been Sanders. This denotes it since both Garret and Gwyn seem to be quite loved in the village and they all go for advice with Garth.
Now with a bit of historical context, something that TObs and I love, before, families had 18 children and 15 died, that's right, partner of the 21st century, the bronze age was brutal, losing a child or two was not Strange, it was rather the rule, whether they were killed, by starvation, by illness or in a criminal trial, as is the case. Keep in mind that Garth used to be a thief and if he stole something from them he was going to be murdered, however sensual the warning may have sounded, now imagine the sentence of an organized kidnapping and apparently many charges of disorderly conduct, added to the fact that It is said that the Marches are a hostile place, possibly equally the Baroness sentence would be the death penalty, having captives or cripples in the village was not a smart option, and as you can see the healing magic of Savarra is not miraculous, Leora she did not fully recover from an injury, another reason why Gweyr wouldn't risk getting hurt.
So I don't think Gweyr is a monster, he just did what any experienced survivor would do.