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 is His slave and Messenger.
Abu Hurayrah narrated that the Prophet said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry; otherwise there will be great mischief and corruption on earth." [Ibn Maajah and At-Tirmithi] Al-Albaani graded this Hadeeth as Hasan.
In this Hadeeth, the Prophet urges the guardian of the woman to accept marrying her off to the religious and good-mannered man who proposes for her. So, you are asked as a guardian to find out all important information about this man's morality and piety. You can do that by first asking him about his prayer and his relationship with his Lord. You should also ask him about his stand from the fundamentals of ethic and morality such as: honesty, frankness, shyness, …etc.
In addition, ask others about him, his friends, colleagues at work, neighbors, or a relative of yours living in Qatar and who can inquire about these things.
If you cannot do that from the place where you live now, then we advise you to come to Qatar and do the job yourself. If you are satisfied with his religion and morals, then accept him as a husband to your sister. But keep on asking Allah to inspire you on the right thing and to guide you to that which pleases Him. We ask Allah to ease your matters and guide you to the right path.
Finally, we thank you for your strong desire to help your sister get that which is good for her in this life and the Hereafter.
Allah knows best.