Pics 1 and 2 are the same fish. Pics 3 and 4 are a different one.
No interactions present.
Brook trout is a North American char (genus Salvilinus as you point out) which hasnt been introduced to this area here. Char species tend to have pale spots on a darker backround while trout species have dark spots on a paler backround. These are indigenous Salmo trutta.
Lat/Lng: 55.005, -6.014
OS grid ref: NW434751