Yes, they can renounce the inheritance in advance. Any legal heir shall be entitled to renounce his right to succession - in whole or in part - in a written agreement concluded with the testator. The renouncement shall not affect the descendants of the person making the renouncement, except if it is so stated in the agreement or if it occurs in return for satisfaction reaching the reserved portion. If the renouncement is made in favour of a specific person it shall only apply - unless the parties have agreed otherwise - if that specific person stands to inherit from the decedent. Any renouncement made by a descendant of the testator shall apply - unless the parties have agreed otherwise - in favour of the other descendants. The renouncement of the inheritance shall - unless the parties have agreed otherwise - also constitute a renouncement of the reserved portion. However, renouncement of the reserved portion shall not imply a disclaim of other titles of inheritance.