As the other person said, the 18.5 lens is a CX lens designed for the Nikon One series of cameras, not your F-Mount D5000.
35mm is mildly wide angle but really won't give you wide angle use on a DX camera like your D5000. The bokeh is just so so on most wide angles and the 35 f/1.8 is no exception. You probably do not want to shoot head and shoulders portraits with this or wider lenses. It will exaggerate facial features by extending the subject's nose, for example.
Bokeh refers to the quality of the background blur when that background is out of focus. You can't say, "I want bokeh," but you can say, "I want creamy bokeh." See the difference?
The 50 f/1.8G is an FX lens and will work fine on your camera, but will have the field of view similar to a 75mm lens, so you have the correct field of view for a portrait lens but not the compressed flattening a good portrait lens will give. This lens produces a little better bokeh than the 35mm lens, but it's not really in league with better glass.
If you're interested in subject isolation and a portrait lens, an 85 f/1.8G is probably where to start. It's a little bit long as far as field of view on a D5000 but that is usually not an issue if you compose tightly like you should. You just might have to stand back a little more. It also will provide that good compression which helps create wonderful portraits along with a creamy enough bokeh. If you just don't have the room or you're shooting larger groups, those other two lenses will be fine with the limitations I mentioned.
Nov 19, 2014 by
Orlando, FL, USA
Orlando, FL, USA
Favorite Subject: Nature
Nikon Family: 21+ years
Experience: More than 20 years
Role: Professional photographer