Short answer. No. Article 818 forbids two or more persons from making a will jointly or in the same instrument, whether for their reciprocal benefit or for a third person's. Your parents must each execute a separate will; one document signed by both is not a valid will for either of them.

What the law says

Two or more persons cannot make a will jointly, or in the same instrument, either for their reciprocal benefit or for the benefit of a third person.

Civil Code, Article 818 — Joint Wills Are Prohibited. Read the full provision →

The prohibition is about the document, not the intention

Article 818 is short and absolute: Two or more persons cannot make a will jointly, or in the same instrument, either for their reciprocal benefit or for the benefit of a third person. Note what the article is aimed at. There is nothing unlawful about your parents wanting the survivor to take everything, and nothing unlawful about them agreeing on it. What the law refuses to accept is the vehicle — one instrument carrying two testators. The clause covering benefit to a third person closes the obvious workaround of a joint will in favour of the children rather than each other.

Why the Code will not allow it

A will is a personal and revocable act until the moment of death. Article 828 provides that a will may be revoked by the testator at any time before his death, and that any waiver or restriction of that right is void. A single instrument signed by two people works against both features at once: it makes one person's disposition depend on another's, and it puts practical and moral pressure on the survivor not to change what the couple signed together. Requiring separate wills keeps each testator free to revise his own until he dies, which is precisely what the law insists on.

Signing it abroad does not rescue it

This is the point families with relatives overseas get wrong. Some jurisdictions do permit joint or mutual wills, and it is tempting to assume a will executed validly where it was made will be honoured here. Article 819 forecloses that: wills prohibited by the preceding article, executed by Filipinos in a foreign country, are not valid in the Philippines even though authorised by the laws of the country where they were executed. The general rule that a Filipino abroad may follow local formalities has this carved out of it, and there is no way around it by choosing a friendly place to sign.

What your parents should do instead

Two separate wills, each executed in proper form, can achieve nearly everything a joint will was meant to achieve — each parent leaving the disposable portion to the other, with substitute provisions in case the other dies first. What separate wills cannot do is bind the survivor, who remains free to change his own will afterwards; if that possibility is the real worry, it is a matter for lifetime arrangements rather than for wills. Either way, the legitimes of the children remain reserved, so leaving absolutely everything to the surviving spouse is not something either instrument can deliver.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.