Hey Jaspal,
To the best of my knowledge:
1 - You can sponsor as long as you are a resident - in the sense that Australia is your place of residence and no other. 5 Months in Oz should be more than enough to fulfil you sponsorship obligations.
2 - You can sponsor your brother..even though your Sister-in-law is the points provider. You being related by blood to your brother will fetch them 15 points and your Sis-in-law will provide the points required and meet the basic requirements.
3 - There are tons of threads here on AOS and plenty is available on the net and the DIMA website. If your friend meets the income criteria for AOS, he can be the butturer. AFAIK, it is $5000 for the couple and you or your family can give it to your friend (if you want) who will then lodge it with The Commonwealth Bank, through centrelink for a period of two years - after that the money will be returned to the butturer (buttuming no untoward incidents happen which makes the federal government to withdraw money from your butturer's deposit)
Do some research about this on the forum and elsewhere and you will get tons of info about it. Hopefully, an expert on this site will read your thread and add more value to it.
Cheers, Orangestreet
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