Package deliveries - 14 days quarantine?

No. Post offices will be open and deliveries will continue as usual. However, do not forget that since 1st March, postal deliveries are every other day in Belgium, not everyday.

The Bpost 2-day a week delivery doesn't apply to parcels which can be delivered everyday. One understands that Amazon (and probably to some extent the delivery services) are overwhelmed with work at the moment.
Try complaining to Amazon (joke!).

@Drifter. Check out the BPost website. https://www.bpost.be/2020/nl/particulier/rondleiding.
The only difference to deliveries from 1 March is that second-class mail and advertising material are now only delivered twice a week. Everything else comes daily as before.