It should be remembered that Ratcliffe will be the single biggest shareholder. In fact, if the Glazers are selling their shares equally (each of them selling 25% of what they own), Ratcliffe will basically own the same as Joel and Avram put together. The other four siblings have never shown any real interest in the club so could very well prefer someone coming in who will run things better, as that will inevitably put more money in their pockets. At which point Joel and Avram wouldn't have too much say in what happens (not sure how much Avram has been involved in decision making anyway, seeing as all the rumours have mostly just talked about Joel).
Also, there were rumours that some of the siblings preferred a full sale, so if that is the case then that's an avenue that Ratcliffe can use to increase his control in the not-too-distant future seeing as apparently he gets first dibs. Of course, that's reliant on the Glazer's selling equally now, rather than let's say the two lowest holders selling all of theirs while the other four continue to hold the same as they currently do.