I'm probably going to say some stuff you already know, but some of this will hopefully be new.
There are many reports of Samyang/Rokinon/Bower lenses suffering from decentering quality issues. Fortunately for you, their 14mm seems to be more reliable than the 24mm. My first 14 was good but I had to return three 24's. Bloated, fuzzy, yet generally round stars are a focus or tripod shake issue. Triangular fan-shaped stars or curving halos are a lens problem.
Some lenses don't have a perfectly flat field, so I find a star around 1/3 of the way between the center and the corner as my focus guide. That gives a good compromise for sharpness across the frame. (If there's no good star 1/3 of the way out, reaim the camera to get a star in that spot, focus, then recompose.)
Focus with maximum liveview zoom. Bright stars are good for rough focus, but too-bright stars might look good even when slightly out of focus. That's why I prefer dimmer start to confirm focus. Ideally, find a star that only shows when in perfect focus, and fades away (because the light becomes too spread) when off.