Conditions for the validity of Salaah

Q: I work in a hospital. The hand rub we use contains alcohol (ethanol) mixed with glycerine. Some drops fell on my clothes and dried. Can I pray with that clothes?

Q: Is wearing a skull cap mandatory whilst praying Salaah?

Q: I had offered 2 rakaahs of sunnah after zuhr, but I forgot that I already offered it. So I offered it again, but I mistakenly faced the wrong direction instead of the Qiblah. Should I offer the sunnah again?

Q: Till what time can one offer fajr prayer? 

Q: Just want to find out which salaah's can be joined (read at the same time) when one is a traveller?​

Q: I read that Maghrib prayer time ends when the redness in the sky goes away. Also I read that it ends half an hour before Isha Azan. Which one is true? Half an hour before Isha azan I feel the sky becomes darker. Can I still pray Maghrib or should I mention as qadha namaz? As I'm a working woman and gets little late to reach home and can't pray in van.

Q: Can we perform salaah with clothes on which has animals like Puma shirts, etc.?

Q: If fajar azan is at 4:45 am then what's the maximum last time tahajjud can be offered?

Q: A lot of people tell me that you can delay isha prayer till midnight, is this true?

Q: If I have filth on my clothes less than the size of a dirham and water touches it and the diameter increases from one dirham, can I pray in those clothes?