http://www.bcphilippineslawyers.com/...ilippines/490/I - Though not incestuous the following between relatives are void from the beginning for reasons of public policy:
1. Between collateral blood relatives, whether legitimate or illegitimate, up to the fourth civil degree;
2. Between step-parents and step-children;
3. Between parents-in-law and children-in-law;
4. Between the adopting parent and the adopted child;
5. Between the surviving spouse of the adopting parent and the adopted child;
6. Between the surviving spouse of the adopted child and the adopter;
7. Between an adopted child and and a legitimate child of the adopter;
8. Between adopted children of the same adopter;
9. Between parties where one, with the intention to marry the other, killed the other person’s spouse, or his or her own spouse.