Changing one's oath

Q: I have made a niyat to Allah Ta'ala and now I am unable to stick to it. I want to make some changes in that niyat. Is it possible to do so? I have heard that Sahaabah (Companions of Nabi Muhammad sallallahu alaihi wasallam)) sometime in their lives broke kasams or niyat and paid kafaraah. May Allah Ta'ala forgive me if I am wrong, let me know if there is any way so tht I can change my niyat and make things easy for me.

Preparing more than one dish of food

Q:

1. Is it an authentic statement in Islam that, if we eat with more than 2 items of food, we have to feed a guest or guests?

2. If anybody cooks and eats with more than 5 or 6 items almost every day, will Allah Ta'ala will like it?

3. And if anybody wastes foods mostly due to cooking too much, that person will be sinful?

4. If a wife's husband always wants to eat more than 5 or more items, but she is busy with her kids and other household works, and her personal prayers, will she be sinful?

Earning money through deceiving people

Q: My husband works for a private company. They give fuel tanks for rent to foreigners. When the fuel in the foreigner's tanks gets dirty and it is of no use to them, the driver takes that fuel and sells it outside the bazaar. This driver is introduced to customers by my husband and my husband does a deal with him to split the profits. Is this money halal for us or not? 

Tying one's ihraam in the plane

Q: I will be leaving for Umrah in a week. I will be landing in Jeddah, and I will have to be in the state of Ihram. I have a few questions regarding going into Ihraam. 

1. I will make the ghusul in South Africa that morning before I leave for Jeddah. Will it be valid if I go into Ihraam on the plane before landing in Jeddah?

If I go in to Ihraam on the plane must I make the the 2 rakaats of Sunnat Salaah on the plane.

2. As mentioned in question 1, if I go into Ihraam on the plane, must I proceed straight to perform Umrah or I may go to the Hotel?

3. As mentioned question 2, if I can go to the hotel and then perform Umrah, can I remove the Ihraam I was in and make ghusal and re-enter in to Ihraam?