Tawbah and repentance

Q: I am a student of Islamic university and I am on my hunt for a serious question. We discussed it with our fellows and class mates but could not find any solutions. The only thing we came up to is that person should die or his matter should be left to Allah. If a boy that is not baaligh has committed zina with his sister not knowing what he is doing he just done it (like he didn't know the punishment or exactly the relation with his sister) then when he grew up he realized what he has done and is ashamed and asks Allah for forgiveness, is their any way he could get free from his dirty sin that he has committed in his childhood? The boy has actually realized and the sin is killing him from inside. Is their any type of kafara or something in our religion that could be done by him to get freedom from his sin?

Names

Q: It is permissible to use an indirect Quranic name. For example, Zayana is an indirect Quranic name for girls that means “adorner”, one who adorns and beautifies something, “adorned”, beautiful, and one who improves things and solves problems. It is derived from the Z-Y-N root which is used in many places in the Quran: "And He [it is who] decreed that they become seven heavens in two aeons, and imparted unto each heaven its function. And We adorned the skies nearest to the earth with lights, and made them secure: such is the ordaining of the Almighty, the All-Knowing. (Quran 41:12)"

Inheritance

Q: I have one son from my late wife and no child from my second wife. My widowed mother is alive and living with my younger brother. After my death how will be my property distributed and who will be the inheritors? Please advice the shariah ruling.

Slaughtering chicken

Q: I want to ask that if during chicken slaughter, the head is mistakenly detached from the body, is the chicken halaal if it was slaughtered according to shariah? Secondly after how much time can it be cooked and prepared?