Customer demanding a refund since a lower price is available on the market

Q: We supplied stock to Muslim owned wholesaler. This is how the transaction went: 

We quoted a price. The buyer was happy and they placed an order of 10 pallets of stock. We arranged the stock, invoice it and supplied it without any problem. 14 days later the client paid. There was no defect in the product. 2 weeks after they paid, the price of this product dropped in the market, so that is nearly 30 days after they placed the order. 

The item sells at R27 and we supplied it to him at R22. Two weeks after he had it on his floor and the price dropped, he contacted us to say that he can get it at R19. 00 and we must pick up the stock or exchange it for another item with a good price. 

What am I allowed to do it the sharia regarding this situation? 

I did say I can drop this price abit and refund you a R2 but he did not sound happy. This will also put me in a problem as now I have to go and collect the stock at my cost and my profit margin was low when doing this deal. 

As a Muslim business man, is he allowed to instruct me to pick up my stock according to how the transaction took place and refund him or send him other stock for that value. What if I don't have a good deal for him at this moment?

Rights of non-Muslim parents upon their Muslim children

Q: What are the rights of our parents upon us as convert Muslims? (Mind you our parents are non Muslims) Since someone said, even their prayers don't help us with anything because they are not Muslims and they are therefore not important to us because they are non Muslims. Is this true? 

Another question is that once you get married and your parents ask you to do something for them whilst your husband refuses, who should you obey? We know Islam says jannah lies under your mother's feet so when it comes to that, which side does the woman take? Does she have to obey the husband and ignore the parents?

Reading Aayat-e-Kareemah

Q: Can I read Aayate Kareema (Prophet Yunus alaihis salaam's dua) everyday 1000 times? 

Can I count it as Istighfaar or Tauba or both? If yes then do I need to do the istighfaar separately or the above 1000 times Aayate Kareema daily is istighfaar as well. 

Does reading Aayate Kareema need ijaazat/permission from any Shaikh, Aalim or Mufti?

Grandfather making a bequest that his house should go to his grandson

Q: Recently in my backyard I built a small cottage for my elderly parents to move into. My father actually built it i.e. he paid for it and alhamdullilah they moved in. So the main house belongs to me as well as the land, only the back cottage belongs to my father. 

I have a 20 yr old son, who my father told him that when we are gone (i.e. my parents), this house (back cottage) is yours. 

Now what happens when my parents leave this world? How does it work with regards to the inheritance etc.? 

And can it lead to problems and what will be the solution? Because my parents will obviously have to live there until they leave this world. 

Women attending Zikr Programs in Masjid

Q: In one masjid on a Thursday night, the imaams conduct a zikr program with various athkaar including durood and some targheeb is also given. However, they have a ladies section in the masjid and ladies are accommodated. People from various parts of town attend. There's also a live streaming link which many listen to. 

What is Mufti Sahebs advise regarding women frequenting zikr majaalis during the night's held in masaajid?