Do the Jinn have anything to do with the disappearance of objects?
Jinn are one of Allah creatures, and whosoever lost anything should look for it and never accuse niether the Jinn nor humans of stealing it. And Allah Knows Best.
Is Hyena's Meat Permissible or Impermissible?
All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
There is disagreement amongst the jurists as regards the ruling on eating hyena`s meat. Shafi`i and Hanabli jurists are of the view that eating hyena`s meat is permissible. The proof is the Hadith related by Al-Baihaqhi on the authority of Ibn Abi Ammar who said: "I asked Jabir bin Abdulla about hyenas, and he told me to eat them. I said: "Is it not game? He said: 'Yes' I said: 'Did you hear that from the Messenger of Allah?" He said: "Yes." And Allah The Almighty Knows Best.
If a woman makes a vow to slaughter a sheep, and her husband is the one who buys it for her from his own money, and he says: "It is for you until you fulfill your vow with it," Is this permissible, or must she buy it herself from her own money?
If her husband gave her the sheep as a donation for the puprose of fulfilling the oath she made and was slaughtered by the wife or the husband on her behalf then the vow she made is fulfilled. And Allah Knows Best.
I suffer from absentmindedness and constant worries during prayer, what should I do?
You should take refuge in Allah from the whispers of the devil and life worries. You should also seek Allah`s help and offer a lot of Istigfar (seeking the forgiveness of Allah). And Allah Knows Best.