Under Article 988 of the New Civil Code of the Philippines (NCC), you and your siblings will inherit everything.
Art. 988. In the absence of legitimate descendants or ascendants, the illegitimate children shall succeed to the entire estate of the deceased.Clarification: The live-in partner of an illegitimate child does not have any right to inherit but is entitled to share in the partnership property under Articles 147 and 148 of the Family Code.
Question: Art. 988 NCC provides that the parent’s ascendants must be legitimate. Let’s say Jose is illegitimate. He has an illegitimate child Rene. In turn, Rene has his own illegitimate child Nestor. If Rene dies, who will inherit - both his son Nestor and his father Jose, or Nestor alone?
Answer: Only Nestor will inherit. One basic principle under the NCC is “nearer excludes farther” which means that the relative closest in degree to the deceased will exclude from inheriting those who are farther away in degree. Another principle in determining who the heirs are is that we go down (descending line) first before going up (ascending line). If there are heirs in the descending line (children or grandchildren), they will exclude those in the ascending line (parents or grandparents). Thus, even if Jose and Nestor are both one degree away from Rene, Nestor (descendant) excludes Jose (ascendant) from inheriting.
 If any of your siblings died before your parent, the descendants (children or grandchildren, whether legitimate or illegitimate) of your deceased sibling will inherit by right of representation while you will inherit on your own right under Articles 989 and 990 of the New Civil Code of the Philippines.
Art. 989. If, together with illegitimate children, there should survive descendants of another illegitimate child who is dead, the former shall succeed in their own right and the latter by right of representation.For example, you have two illegitimate siblings. If all three of you are alive, then you divide your parent’s estate by three. Let’s say, however, that one of your siblings, who has four children, died before your parent. You still divide the estate by three; the four children will divide among themselves the share that should have gone to their parent (your deceased sibling).
Art. 990. The hereditary rights granted by the two preceding articles to illegitimate children shall be transmitted upon their death to their descendants, who shall inherit by right of representation from their deceased grandparent.
Situation B: What if your parent had illegitimate children from different partners?
Same answers as above.
Situation C: Your parent died with no spouse but with legitimate ascendants (parents, grandparents, or great-grandparents).
 You will share the estate with the ascendants on a 50-50 basis under Article 991 of the New Civil Code of the Philippines.
Art. 991. If legitimate ascendants are left, the illegitimate children shall divide the inheritance with them, taking one-half of the estate, whatever be the number of the ascendants or of the illegitimate children.For example, a person dies leaving one ascendant and five illegitimate children (whether from the same partner or different partners). The ascendant gets 50% of the estate, while the five illegitimate children will divide among themselves the other 50%.
 What if there are several ascendants left, for example, the father or the mother, and both grandparents? Will the grandparents also share in the inheritance? Based on the principle of “nearer excludes farther”, they will not inherit.
Situation D: You are illegitimate; your parent died with no ascendant but with one legitimate sibling. If that sibling died after your parent, can you inherit from this sibling by stepping into your parent’s place?
No, you cannot claim any inheritance from your parent’s sibling under Article 992 of the New Civil Code of the Philippines.
Art. 992. An illegitimate child has no right to inherit ab intestato from the legitimate children and relatives of his father or mother; nor shall such children or relatives inherit in the same manner from the illegitimate child.This is known as the iron barrier between the legitimate and illegitimate sides of the family. For the same reason, your parent’s legitimate sibling cannot inherit from you.