Your earn was permanently sealed with an epoxy sealant that may not be able to be removed, especially without damaging the urns.
The first thing to do is to find out what epoxy compound was used to seal the earn. If it had an acidic base, then your urn is permanently welded shut. You would have to drill a whole which could be resealed later.
If it was a non-acid based epoxy, then chemical welding of the brass would not have occurred. You can find an epoxy solvent and drip it into the joint, and over several days, the epoxy will most likely dissolve enough to open the urn.