Qasar Salaah and Full Salaah

Will a person who has two houses in different countries perform full salaah or qasar salaah?

Q: I lived in South africa for many years, then for some reason I moved to another country with my whole family. However, I still have my house in South Africa and I have the intention to come back and live in this house after a few years.

My question is that if I come to my house in South Africa for 3 days just to see if everything is alright, will I be a musaafir or not?

How should a Musaafir calculate if he has to perform full salaah or qasr salaah?

Q: How can I calculate 15 days during a journey in order to know whether I need to perform qasar Salaah or full salaah. Suppose I reach a destination on 1st Dec 05:30 pm and plan to stay till 15th Dec 05:30 am.

Do I need to to take into account till 15th Dec 5:30 pm (360 hrs) as it is less than 360 I should offer Qasr even though it is 15th day ?

Musaafirs intention changing before 15 days

Q:

1. If a person intends to stay for 15 days and perform full salah but leaves on the 14th day to a different city which is 10 miles away from the first city for 3 days and comes back to stay again in the same city for more than 10 days. Should be perform qasar salaah or full salaah in all the cities?

2. If a person intends to stay for 14 days in one city and performs qasar salaah but his stay extends by a day or two and then he leaves to a different city which is 10 miles away from the first city for 3 days and comes back to stay again in the same city for more than 10 days. Should he perform qasar salaah or full salaah in all the cities?