If a permit is required for the renovations of your neighbours, you can object to the municipality or submit an opinion to the municipality. You have to do so within the fatal deadline of six weeks after the publication of the (draft) decision. Make sure to keep a close eye on the municipal announcements. You can find them on the municipal website or in the free local paper.
In the notice of objection/opinion you explain why and that you do not agree with the building plans. If the objection/opinion fails, you can appeal to the court and, if necessary, to the Administrative Jurisdiction Division of the Council of State.
Some renovations, for instance a dormer at the back of a building, are not subject to a permit requirement. If you do not agree with these plans, talk to your neighbours and try to work it out together.