u should create sone middle ground with ur in laws as it may cause unrequired tension at this busy time- and for them to feel that your side is being too much 'in control' over their side of the preps. Ideally most brides would love to pick out there own dress/jewellery and get the in laws to pay.
i think u should wait for them to start discussion on this matter, and then ease in ur point of view, this may come across as more thoughtful.