Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- As long as you are sure the man who sired you is your biological father, you are a legitimate son of your parents.
2- Hence, you are allowed to inherit your father and your aunts are mahrams to you.
3- You should not dig in such old matter as you are not to judge your parents; leave such matters for Allah Almighty.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
There is no need for you to dig into this matter further. Whatever happened between your father and mother is a matter between them and Allah; we are not allowed to dig into it and make judgments; let Allah be the judge.
The Prophet (peace and blessings be upon him) said, “Avoid these filthy practices which Allah Almighty has prohibited. If one commits any of them, he should conceal with Allah’s Most High Veil (i.e. should not speak about it), and should turn to Allah, the Most High in repentance.” (Al-Hakim)
Concealing with Allah’s Veil means not to dig into peoples’ past, especially the dead.
In conclusion, you are born in marriage and, therefore, you are allowed to inherit your father who sired you.
Allah Almighty knows best.