Short answer. No. A fideicommissary substitution can never burden the legitime. The reserved share the law guarantees your compulsory heir must pass to that heir free and clear; you cannot tie it up with an obligation to preserve it and transmit it onward to a second heir. Such a substitution can reach only your disposable portion.
What the law says
A fideicommissary substitution can never burden the legitime.
Civil Code, Article 864 — It Can Never Burden the Legitime. Read the full provision →
The legitime is off limits
Article 864 states an absolute limit: a fideicommissary substitution can never burden the legitime. A fideicommissary substitution is the arrangement by which a first heir, the fiduciary, is obliged to preserve the inheritance and eventually hand it on to a second heir. That obligation is a genuine burden on the property, it ties the first heir's hands and postpones full ownership. The law forbids placing that burden on the legitime, the portion the Civil Code reserves for compulsory heirs. Your child's legitime must come to him as his own, not as property he merely holds for someone else.
Why the reserved share is protected
The legitime exists precisely to guarantee compulsory heirs a minimum they take freely and absolutely. Allowing a fideicommissary substitution over it would hollow that guarantee out: the heir would receive the reserved share in name but be unable to use or dispose of it, bound instead to keep it intact for a second heir. That is ownership stripped of its substance. So the prohibition is not a technicality but the mechanism that keeps the legitime meaningful, ensuring the protected share is enjoyment, not mere custody.
Where such a substitution can operate
The bar applies to the legitime, not to the whole estate. Over your free or disposable portion, the part you may give to whomever you choose, a fideicommissary substitution is permissible, provided its other requirements are met. So you can set up a first-heir-to-second-heir arrangement using the property you are free to dispose of, while the legitime of each compulsory heir stays clear of it. The distinction is between the reserved shares, which the law fixes and shields, and the portion left to your free disposal, where you have room to build such structures.
What this means for your plan
If you want to route property through a first heir to a second, identify what falls within your disposable portion and confine the substitution to that. Any attempt to lay it over a compulsory heir's legitime is void as to that share; the heir takes the legitime unburdened regardless of the clause. Because the size of the legitime and of the free portion depends on who your compulsory heirs are, work those figures out first. A lawyer can tell you how much of your estate is actually available for a fideicommissary arrangement.