As LIZS says, your argument has to be for a school, not against one. Saying anything about the OFTSTED, reputation etc of the other school is irrelevant, and will get you nowhere at appeal (and may work to your detriment, if one of the panelist has a connection to or a child at that school.)
The FAP isn't relevant either, as it sounds as if there is a place available at a nearby school, it's just one you don't want. The FAP would only be relevant if there were no spaces in a reasonable distance.
You need to make the case that the detriment to the school of taking another pupil is less than the detriment to your DSC in not getting a place. Focus on things this school offers that supports their needs specifically - the sport, for example, is something you should definitely mention, as well as the English support. Do they offer any relevant other languages? any other clubs -for example, is there a wellbeing club that might be helpful for a child new to the UK?
Being on the same campus as their step siblings is worth mentioning too, especially in the context of the child being new to the country and not speaking the language. It's not a big thing, but it's all part of the picture.
Part of the argument will also be chipping away at the school's case for being full, which you should get before the appeal, but will normally revolve around only being set up for 30 in a form/science rooms being too small/no lunch space etc etc. Here one of the main questions is have they gone over PAN in other years, as this shows they can cope with more. if they are already over PAN in yr 7 though (as opposed to at PAN), this can make it harder to persuade a panel they can cope with more.