Lowering the back for ruku' and sajdah when performing salaah while seated on a chair

Q:

  1. When performing salah sitting on a chair do you leave your back straight and just move your head little for ruku and more for sajdah as mentioned in the video by the mufti saheb or you should move the back as well, because that's what I have seen people even scholars pray who are unable to do ruku and sajdah and the in a normal manner? Link: ...
  2. If the mufti saheb in the video is correct how is it for a person who is unable to do sajdah on the ground to move the back when praying sitting on the chair or on the ground?

Women performing Salaah in the haram

Q: I am currently in makkah and in the haram there are ladies reading everywhere amongst the men and also at times there are so many people that I have to read on the second and the third level. Is salah valid even though there seems to be no continuity of the saffs? Also if there would be a row of ladies reading salaah in front of me or next to me or on a level below me behind the Imaam and I am also following the Imam, what is the status of my salaah? Since I was unsure I have been repeating my salaah individually after every salaah.

Sunnah method of dua after Salaah

Q: In our area, the Imam starts to make dua with such a voice that muqtadi could know that Imam has started to making dua and all the muqtadis start making dua after listening to the voice of Imam (e.g. if he starts dua with alhamdulillahi rabbil a'alameen, he says alhamdulillahi...... with voice and then make entire dua silently). He ends the dua with voice so that muqtadis could know, and muqtadis also end their dua after listening to his voice. No one starts making dua before and none completes dua before the Imam. What is the shar'ee status of this all described above? Should the muqtadi not start making dua before the Imam? Should the Imam inform the muqtadees about his dua by starting it with voice or he should starts his dua silently? If one has finished his dua before Imam, should he wait until the Imam finishes or one should he stand up to offer the sunnats (if there are sunnats after that fardh salaah)? Please clarify the questions and the Shar'ee status of the custom of dua described above.