More thoughts for you Sylvia...
One of the benefits of homeschooling in terms of socialization is that children learn to interact with all ages. For me it was beneficial to learn from a variety of older adults who were master gardeners, scientists, artists, writers--you can see the types of circles you need to develop. Also, my brother and I were in play groups with other children--we had time to just be! I have retained many of the friends from that time, going on twenty years of contact.
Children also develop less of a "group mentality" which I am sure parents on the board can attest to being a somewhat annoying character trait. Fads and trends do not have to be catered to. Students can focus on their individual strengths. Achievements are not compared on a large scale, allowing a student to feel successful and gain confidence.
Enrolling in "extracurriculars" serve the social purpose of recess, lunch, and class time in a traditional school. The amount of social time I have to effectively turn in to knowledge acquisition in a traditional classroom (remember I am a certified teacher) is, I assure you, overhwelming at times, esp. with teenagers.
The guidelines for what you are required to teach are very clear. The ministry of eduation knows exactly what it wants to see in a graduate. If a homeschool student can work this to their advantage, it becomes a very easy process of meeting the standard. For my part, I always finished my assessments very quickly because I learned that the time left over was my time to be creative. My brother might spend six hours a day at school work and I spent 4, meeting the same standard.
Be aware of standardized tests which your kids must take. In the States it ranges from the SAT, to the ACT, to the learning results for individual states. In Europe they have A-levels, right? Know now what is on the exam. If the kids need an eight week prep course or something, you can handle it.
Foreign languages are required at university and undoubtedly your kids will test out of this requirement. Ideally you will expose them to a third and fourth language, like German, Japanese, Chinese, French. I wouldn't sweat this component one bit since they will be able to test out at university.
Math is very important depending on the career! The sciences, too, of course--maybe you can enroll them at local colleges before they take exams in these areas. They may not be university-quality as you know it, but they will undoubtedly prep your children for the next level, especially if you get them in early, like 16 and 17. Chemistry, physics--the higher maths and sciences especially are good to be exposed to in different situations.
For literature and grammar, there are several excellent courses of study available. This will turn both teacher and students into readers and writers. The dialogue between teacher and students becomes very advanced because of the sheer focus of the situation.