A tip once you get your bottle of brush on glue...
Trim the brush on an angle to make a fine point. Something that will help, cut the brush from the FRONT, not from the back of the brush. So hold the brush so the tip is facing you and cut with some sharp scissors from your side to the handle. If you cut from this direction, the bristles will cut and not just push out of the way like when you try and cut from the other direction.
I usually will clean the brush off with acetone to get all the superglue off before trimming, but you can do it with glue, just clean your scissors quickly afterwards.