Visa on arrival.... if your brother-in-law belongs to the 33 prefered, rich & developed nations,( UK,USA, GCC, Japan,Canada etc.etc)
If not three options: 1) Hotel visa 14 days( eg.QR.750 from Gulf Horizon hotel) can be extented with additional charges.It will take 4 working days, The best option.

2)Personal Sponsorship: from Madina Khalifa passport office. For this your wife also must be a resident of Qatar. You also need letter from your employer, your passport copy, QID copy, your wife's PP copy, QID copy, and PP copy of your Brother-in-law.
CostQR 250-300/month)
( One month valid visa which can be extented upto 6 months)
But its very,very,very unlikely that the Captain who sits at the Expat affairs will endorse it.Try your luck.

3) Business visa/ Free visa(valid for one year
If you know the right people you can buy visas.
Very costly ( Qr. 2500- 25,000) depending on the type and duration of stay.