How to connect double swith with 4 wires

There is one simple answer to this.

If you don't know and don't have access to testing facilities which would help you establish the correct connections, then call in an expert - they are called "electricians".

The colour coding of Belgian electrical connections is confusing to amateurs (and has changed comparatively recently) although the earth wire on any modern-ish installation should always be yellow with green stripes. I know what I am doing but I still need to use testing equipment to check precisely what the function of each wire is - and that I have tripped out the right circuit before attempting any rewiring work.