Short answer. Yes. The first heir, the fiduciary, is obliged to deliver the inheritance to the second heir. He may deduct only what arises from legitimate expenses, credits and improvements, unless the testator provided otherwise. And the whole arrangement is valid only if the fideicommissary substitution was expressly made.
What the law says
The fiduciary shall be obliged to deliver the inheritance to the second heir, without other deductions than those which arise from legitimate expenses, credits and improvements, save in the case where the testator has provided otherwise.
Civil Code, Article 865 — It Must Be Express. Read the full provision →
The duty to deliver
In a fideicommissary substitution the first heir is not a full owner but a fiduciary holding for another. Article 865 makes his central obligation plain: the fiduciary shall be obliged to deliver the inheritance to the second heir, without other deductions than those which arise from legitimate expenses, credits and improvements, save in the case where the testator has provided otherwise. He must preserve the property and, when the time set by the testator arrives, transmit it to the second heir. He cannot keep it, and he cannot defeat the second heir's right by treating the inheritance as simply his own to consume or dispose of.
What he may deduct
The fiduciary is not expected to hand everything over out of his own pocket. The article lets him deduct what arises from legitimate expenses, credits and improvements. Legitimate expenses are the proper costs of preserving and administering the property; credits cover sums owing to him in connection with it; improvements account for value he lawfully added. These deductions recognise that holding and maintaining property costs money, and that the fiduciary should not be out of pocket for having conserved the inheritance for the person who ultimately takes it. Beyond these categories, he delivers the inheritance intact.
The testator can adjust the terms
The permitted deductions are a default, not a straitjacket. The closing clause, save in the case where the testator has provided otherwise, lets the testator vary what the fiduciary may retain or claim. He might allow the fiduciary more, or restrict him further, according to the plan he had in mind. So the starting position is the statutory list of deductions, adjusted by whatever the will specifically directs. Reading the will's own terms is therefore essential before assuming the bare default applies.
It only works if expressly made
None of this arises unless the fideicommissary substitution was set up expressly. The same article requires that every fideicommissary substitution must be expressly made in order that it may be valid. A vague hope that a first heir will pass property on, or an arrangement merely implied, does not create the fiduciary's binding duty to preserve and deliver. So the first question is whether the will genuinely established a fideicommissary substitution in clear terms. If it did, the duty to deliver and the limited deductions follow; if it did not, the supposed first heir may simply be an ordinary heir.