All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
No doubt, what you committed is a great and repulsive sin. Incest is a grave major sin. How could it be imagined that a brother rapes his own sister! He should be the one who protects her, fears for her, and guards vigilantly her honor and dignity. Moreover, you did not stop this evil but you continued to have illegitimate relations with other women. Truly to Allah we belong and truly, to Him we shall return.
There is no way for you except making sincere repentance and feeling deep sorrow for previous sins; it is only by doing so that you can purify yourself from these sins.
Furthermore, you should cover yourself and your sister as well. The Prophet said: "Avoid these filthy things [sins] which Allah has forbidden, but if anyone commits any of them, then let him conceal that which Allah has concealed, and let him repent..." [Al-Haakim and Al-Bayhaqi, and Al-Albaani classified it as authentic]
Moreover, you should avoid all the means and motives of Zina (fornication or adultery), such as mixing with women and being with bad company. Instead you should befriend pious people and keep yourself in their gatherings.
Allah knows best.