If they're all going to the same HR/recruitment person, then one letter and one cv would be sufficient.
However, the cover letter contents now would be even more important than normal.
You could indicate your interest in all three, but I would guess that there would be one of the three that you'd be most interested, best qualified, most interested in.
This should be highlighted, with some sort of comment then around the fact that should the also consider appropriate, you would also like to be considered for the other 2, and if the part time one is last choice, highlight this.
Also, if it particularly the company that interests you (as in you'd take any job that they're offering), then you should find words around this as well to show them that you're keen. Phrasing is important here.