Firstly, going to tribunal and appealing the EHCP are the same thing. You have 2 months from the date of the letter or 1 month from the mediation certificate to submit an appeal to SENDIST. If your right of appeal has lapsed, you could ask SENDIST if they will allow leave to appeal out of time, but it isn’t guaranteed.
What is your preference? What do you think? If DS isn’t able to cope in class, secondary MS is unlikely to be suitable.
Are the mainstream schools you originally preferred wholly independent? If not, you don’t need an offer of a place for them to be named. They can be named even if they object. If any of these schools are still your preference, you can appeal for them and there are limited reasons that can be refused.
Is 1:1 detailed, specified and quantified in F?
The school is named, so they can’t say DS can’t attend.
As well as schools in your town, have you looked at schools out of area?
Unless the school is wholly independent, on its own, a school being full isn’t enough of a reason to refuse to name your preferred placement.
Is the independent school that may work wholly independent or a section 41 independent? I suspect wholly independent because I don’t think there is a s41 school that only opened in September 25. In which case, is the school willing to offer a place? For wholly independent schools, you will need to show the LA’s proposed school(s) can’t meet needs &/or it isn’t unreasonable public expenditure. You will need evidence.
There is no guarantee the LA will agree to hold an early review. Even if they do, they may not agree to make the amendments required.
Be careful with SENDIASS. Some are good but too many repeat the LA’s unlawful policies. IPSEA and SOSSEN are better for accurate information.