Performing Salaah in one's underpants

Q: I visited a senior sheikh in Cape Town who qualified in Al Azhar Egypt. The sheikh asked me to stay the night at his house. We made fajr salaah at his house in his study. I gave the iqamah and the sheikh walked into the study and led the salaah as the imaam. Only the two of us were present. The room was dark and after we had completed the salaah the light was switched on and I then only realised that the respected sheik led the fajr salaah in his underpants and a pyjama top. I was taken aback and asked the sheikh if its correct to lead salaah whilst only wearing an underpants and no long pants. The sheikh answered abruptly by saying " are you greater than Imaam Shafee and do you know better than Imaam shafee" I want to know if this was correct to make salaah in an underpants and do I perform my fajr over again as he was the imaam.

Reciting Ta'wuz and Tasmiyah before reciting an Aayat in kitaab reading

Q: When reading a kitaab, like Fazaa'il-e-A`maal for example, one often comes across a single verse or several short verses of the Qur'an Shareef being quoted. (1) Before reciting such a verse, must one recite Ta'wuz and Tasmiyah? (2) Can one just read the English translation below the verse and not the actual Arabic verse itself?

Rinsing the bucket after washing impure clothes

Q: My parents do not understand about najasat much. They clean the impure and the pure clothes together in the same bucket and later they do not wash the bucket and use it again for washing purposes. I have told them that the bucket becomes impure and has to be washed before used again but they are not listening to me and scolding me. When I talk about this now my exams are getting over and I have to go to my home and they wash the clothes the same way as they used to. So if I go and pray with the same clothes after knowing that they are impure will it be kufr and what should I do? Advice me.

Impurity on the floor

Q: When I was in my home many years ago semen got onto the floor (not tiles but smooth floor). I knew nothing about najaasat and all so I just wiped it off with dirty cloth and there was no trace of najasat over there then and later the floor was cleaned with wet cloth and the same cloth is used for cleaning the whole house. Does this make the whole house impure? And if so then the water on the floor which gets absorbed or dried make the floor pure again? If not what should I do now?

Hair dye

Q: I want to ask that if I dye my hair using ordinary dying agents available in the market, would it be an obstacle for my wudhu? Moreover, is it permissible to use dye in black colour?