Short answer. Generally yes. Article 865 lets the fiduciary deliver the inheritance to the second heir with deductions only for legitimate expenses, credits, and improvements, unless the testator provided otherwise. Taxes and genuine upkeep costs he actually paid on the property normally fall within that allowance.
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 →
Delivery is the rule, and deductions are the narrow exception
Article 865 requires the fiduciary to actually hand the property over — that is the point of a fideicommissary substitution — but it also recognizes that a fiduciary who held and managed the property for years may have genuinely spent money on it. 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. The default is delivery in full; deductions are the exception, and only specific categories qualify.
What 'legitimate expenses, credits and improvements' covers
The article names three categories your brother can point to: legitimate expenses, such as real property taxes actually paid to keep the property in good standing; credits, meaning genuine amounts owed to him arising from the property; and improvements, meaning value he actually added to it. Ordinary upkeep that preserved the property, and taxes that had to be paid to avoid penalties or loss of the property, generally fit within legitimate expenses. What does not qualify is spending that was not necessary, or that simply reflects how he chose to use the property for his own benefit.
The testator's will can override this default
The deduction allowance is not absolute — it applies save in the case where the testator has provided otherwise. If the will that created the fideicommissary substitution addressed this question directly, for example by directing that the property pass to you without any deductions at all, that instruction controls over the general rule. Check the exact wording of the will before assuming the default allowance for expenses applies.
What this means for the handover
Practically, your brother should be able to show what he actually paid and why it qualifies as a legitimate expense, credit, or improvement, rather than simply asserting a deduction. You are entitled to see that accounting before accepting a reduced transfer. If the two of you disagree about whether a particular cost genuinely falls within the article's categories, that is a factual dispute about the nature of the expense, separate from the basic rule that only these specific categories can reduce what he must hand over.