Taking an oath in the mind

Q:

1. If one takes an oath in the mind, is it valid? Suppose if we realize that our oath is invalid (oath on not to do something etc) is it necessary to keep up our oath?

2. If we take an oath by saying 'Allah qasam' does it mean oath or promise and even if we take by that word is it valid if we say it in mind?

3. I do not want to take an oath on particular things but if I make it against my will without making up my mind (to say like I feel like I took an oath in mind within 3 or 4 seconds against my willing) but I think I didn't take it intentionally but I feel to be not sure also. In this case should I keep up my oath or no need?

4. Does an unwilling or unintentional oath or promise count?

Can a girl marry her foster brother?

Q: My question is my sister who is in love with her khala's son but the problem in their marriage is that once she was crying in childhood so her khala made her drink milk from her own, so we consulted many Maulanas. They rejected their marriage. So we then approached to Jamie (bhatkal) they suggested it is possible in the Shaafi'ee mazhab but not in the Hanafi Mazhab and we belong to the Hanafi Mazhab and the main problem is they are madly in love. Please suggest me solution as early as possible.

Nikaah

Q:

1. How many farz, wajibaat and sunnat are there in nikah?

2. Which month, day is better for marriage according to Islam?

3. Is there any dua to get a pious, kind, helpful, caring, loving and best mannered girl in nikah?

4. Please inform me about some books regarding nikaah in Islam.

Taking out life insurance to save tax

Q: Here, in South Africa, when a person passes away, he has to pay 20% estate duty of his total estate to the government. Many a time, this amount runs into millions and is an extremely exorbitant amount to pay. I was recently advised by a colleague to take out life insurance so that upon my death, the policy payout will cover the estate duty. Please advise if doing this will be permissible.