Should vowed fast be offered in consecutive days, or not?
Vowed fast should be offered in line with what was originally intended by the vow-maker, either consecutively, or not.
Is the Saum(Fasting) of someone who ate and drank forgetfully while offering fasting of oath expiation invalidated ?
Whosoever eats, or drinks forgetfully is exempted by Allah; therefore, he/she shouldn`t break their fast whether it was obligatory, non-obligatory, or expiatory.
Is committing Zina (Adultery and extramarital sex) without the intention of getting pregnant or deflowered considered full Zina?
All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The Messenger of Allah (PBUH) says: "The eyes commit fornication, the hands, the feet, and the private parts." [Musnad Ahmad, P.3912]. Sheikh Shu`aib `Arn`oot graded this Hadith as sound. What you are asking about is far graver. Generally speaking, sincere repentance erases sins, good deeds erase bad deeds, and fearing Allah stops one from committing this heinous act. In addition, the devil is man`s worst enemy and whoever surrenders themselves to the wolf will be eaten. And Allah The Almighty Knows Best.
Is it permissible for the big brother to force his sisters to wear Hijjab(Islamic wear) if their father didn`t do his part in this regard ?
The father`s attention should be drawn gently and politely, and the sisters should also be reminded with good words since Allah, The Almighty, says: “O ye who believe! Save yourselves and your families from a Fire whose fuel is Men and Stones.”{Al-Tahreem/6}.