Is it compulsory to follow the advice of a doctor?

Q: My question is regarding recent time of crisis when some of my fellow Muslims deny the lockdown and go to masjid. I try to convince them but need a proper basis. Somewhere I read, that it is mentioned in hadees, that If a person goes against the saying of doctor and eats prohibited things by doctor/expert which result to his death, it will be considered as suicide. Is it true? If yes, where is it mentioned.

Sharing in the profit as well as the loss in a mudaarabah contract

Q: I wish to do mudaarabah with a friend. I am the active partner. If I make a profit it'll be shared according to the percentage of profit agreed between us. However if I happen to make a loss, I take the responsibilty of returning the sleeping partner's money (capital). I take this guarantee. Is this halaal. If not please guide us to a legitimate way.

Reciting "Salloo fi buyootikum" in place of "Hayya alas Salaah" and Hayya alal Falaah"

Q: Nowadays, masaajid being closed, azaan is a bit modified. In place of Hayya alas Salaah, Hayya ala Falaah, it is said, Salloo fi buyutikim and salloo fi rihalikum. Is it permissible to change azaan and was it done in the era of Sahaabah (radhiyallahu anhum)? How should we reply to these words?

Studying in school, college or university with non-mahrams

Q:

1. Is it permissible for a man to study in a school, college, or university where he is studying alongside a non mahram woman. And is it permissible for a man to teach a non mahram woman and is it permissible for a woman to learn from a non mahram man.

2. Is it permissible for a woman to study in a school, college, or university where she is studying alongside a non mahram man. And is it permissible for a woman to teach a non mahram man and is it permissible for a man to learn from a non mahram woman.