About the red dragon, the stats and size make it an adult one which is listed as a challenge for level 17 parties (note, challenge means beatable with about 20% resource usage but not in danger of dying). So a level 13 or so party could still kill it but it would be a close call.
A level 3 or 4 party killing it only shows how screwed up Larians combat system is.
Is it supposed to be an adult red dragon? If so, it's kinda lame. This is how a red dragon should look like-
https://i.ytimg.com/vi/IbnQ2UhjgqQ/hqdefault.jpgIt is.
When you examine the dragon you see its statistics (also something that should not be possible) and they match the statistic of an adult red dragon exactly. Also it is huge sized, both in its statistics and in the cutscene which only adult red dragons are.
Thats also not correct, only young dragons work for the Gith, but that would be only as large as horses so Larian probably upgraded them for looks.