When an IB is too difficult (Budapest)

We are a family moving to Budapest this summer with 3 kids.
Our oldest son, 17, has only 1 year from gymnasium in Denmark.

His skills are not good enough to get accepted at the IB course (in grade Protected content AISB - and apparently the high school diploma classes at AISB are taught on IB level...

Does anyone know where a 17 years old boy can get a high school diploma in Budapest - or another education on that level - without the best grades in the world, but a good level in English?

Hope that someone in here has a good advice.