The articles weren't clearly defined here by the sounds of things so revert to shareholding. Personally I've never involved myself in any business where a shareholders' agreement does not exist, so I'm not 100% clued up here. You'd absolutely know better than me here.
A company -has- to have an articles of association. So by all sounds of things, they used the standard Table B articles. Therefore there is some ground rules in existence (which aren't necessarily well developed as a shareholders' agreement would be). I suggest pulling this out and having a good read!
Although DJ... it sounds to be to be the opposite: They have a minority equity stake in a company with no board representation i.e. they are screwed. Personally I wouldn't do anything. Though I am not sure what commercial arrangement OP wants to reach? First step...speak to them and find out their intentions.
Also, unless I missed something, I don't see anything pointing that they would be a section 53(b) company?