Shirk

Q: There are many hadiths which speak about how the shirk that the Sahaba used to do before accepting Islam such as worshipping idols and their other sins have been forgiven once they accepted Islam and became Muslims. Obviously, anyone who was never a Muslim before will be forgiven no matter what did they did in the past once they become Muslims because they didn't know about Islam before. But are there any authentic hadiths which talk about a Muslim committing shirk and being forgiven by Allah even after being a Muslim. Are there any hadiths about a person who is a Muslim and leaves Islam by committing Shirk but Allah still forgives him. I don't think I came across any hadith that speaks about a Muslim being forgiven for shirk, only for non-muslims being forgiven for shirk once there Muslim. Can you give me an authentic hadith that say Allah forgives a Muslim who does shirk and also verses from the Quran if it says this? I'm specifically talking about a Muslim who does shirk and is forgiven, not a non-muslim who does shirk and is forgiven when he accepts Islam. Please give me any references that specifically says this.

Renting a house

Q: We have seen a house, which we like to rent, but we found out that the last people who rented this house were prostitutes! Is it alright to move there and read prayers in there?

Equality towards Children

Q: Would a father be sinful for giving some of his children more money than others - for example financing the trip of one child to go abroad but not giving any money to the other child? Another situation might be the father giving one child thousands of pounds for their studies and giving nothing to the other child. Or does Shari'ah allow a father to give one of his children more money than others (whilst the father is still well and alive)?

Wind problem

Q: My question is that while praying namaz, I release gas frequently. According to deobandi hanafi maslak, can I keep praying namaz with that same wudhu or I need to break my namaaz and do wudhu again and start praying namaz again?

Gargling the mouth and cleaning the nose

Q: When you do ghusl, do you need to make sure you make the gargling noise when rinsing your mouth to make sure you rinsed your mouth correctly and properly? Because it feels embarrassing when you make the noise because other people can hear you outside the bathroom and they would know that I'm doing ghusl and I'm impure? Also, do you have to sniff water up your nose and touch/reach the beginning of the hard bone/part of the nose or is just putting water without sniffing ok because I find it hard and impossible to actually sniff the water into my nose? Also for ghusl, are you allowed to first take shower and rinse your mouth and nose while you're taking a shower? Does this count as ghusl and is it valid?

Dua for protection

Q: I have a friend who reverted recently. He's a native African who's been separated from his mother for a long time. She's said to have this "calling" to be a "sangoma" which in his terms is a medium for communication with spirits. He says the "spirits" now worry him and he sees them. What should he do? Is this even possible since we cannot see the jinn? And if its not jinn then it can be nothing else right? But his mind is playing tricks on him right? I did advise Ayatul kursi and Suratul naas.