There isn't really any "protocol" involved, some people choose to only wear one clan tartan, some people choose to wear a selection of family related tartans,and some wear what they choose because of colour/design/availability. So the answer is really only down to you and how you feel about it. If you find something that you like it's a good idea to find out a little about the tartan concerned, but frankly over the last 8 years of wearing different kilts I have yet to be questioned in any way other than the name of the tartan, so I don't think that you will have much of a problem with whatever you find.I would think if a fellow clan member see you wearing his family one , he is much more likely to be pleased than offended!