There are quite a few flaws in your way of thinking.
Read also this thread: education "tracks" in grade/high school
- It's not you choosing a good lycée, it's the lycées choosing students with good grades.
- International schools can be very different from each other, from a gated reserve for the world's richest brats to perfectly normal schools for students with working parents.
- Students don't choose between English and German, they have both.
- Public school not having equal level is a huge flaw: There are several kinds of schools for different kinds of education and not all are high schools preparing specifically for university studies. The difference is not about level but about the nature of education.
- There are two main factors deciding which school students end up in: Grades and their level in languages including the local one.
- If your children never had two second languages in their education, transfer into Swiss public school is tricky.
- If the goal is to study in an English speaking university like in the UK, US or Australia, coming from the Swiss public system will make the applications difficult and they will only recognize the Maturité. The English speaking world know the IB far better and applications are dealt with by the school, which is a help you don't want to miss.
- If the goal is to study in Switzerland, local language and grades in lycée (maturité) is the key. Your children have to be accepted in a lycée in the first place.
- There are quite a few schools, international and private, around Lausanne, you might consider looking in Vevey or Coppet, Morges etc on both sides of Lausanne along the lake.