I believe football teams in the past have received sanctions where their fans have engaged in anti-social or violent behaviour. I think the same should apply here. Those who are organising the "protest" should be refused entry to the grounds. If the protest starts at 9 seconds, the match should be suspended immediately. The club also should issue the strongest possible statement distancing themselves from this action and from the convicted rapist as well.
It may be hard to believe the man's girlfriend is standing by him, but I am sure we have all known women who have "stood by their man" even when they have experienced the most hideous abuse, humiliation and/or deception from them. It is possible that she has bought the garbage that women literally throw themselves at professional football players, that being "red blooded men," they are incapable of resisting such advances and therefore, it is impossible that they could "genuinely" rape anyone. Papers like the Daily Mail are filled with stories of women who lie about rape, which also supports this position. Perhaps the girlfriend just feels she has to accept infidelity as an occupational hazard of being in a relationship with a professional footballer.
I suppose I can somewhat understand the sister's support for her brother. It's not the first time that someone has believed a relative despite overwhelming evidence that they are lying.