I used to stay overseas with my family for a couple of years and moved back to Singapore about 3 years ago. During our time there, my dad was doing quite well with his job and all. However, I did notice that my neighbour had a feng shui master. Everything was fine until my final year overseas. My neighbours started to make very drastic changes to their house (as directed by their fengshui master). 

They hung lighted lanterns outside their door, they bought a huge rock fixture, they started burning a lot more incense paper, they changed their cars, renovated their house, grew their hair longer etc. After relocating back to Singapore, my father has been struggling with his job and has yet to find a source of steady income. Recently, my mother found a job but it is over stressing her. It has been a downhill for my parents. Is it at all possible that my overseas neighbour were tapping into our good chi and still continue tapping into it? 

If so, how can we prevent it / claim back that good chi? I apologize for this long question but I would very much appreciate your help as I wish to help my family out of this. Thank you very much!

I am quite doubtful that your neighbor has set up their Feng Shui to steal your house's Qi. No ethical FS practitioner would do such a thing. 

The problem could be that the Annual Sha Qi has been activated by external changes in your home. And hence when you move back in, you have these problems. 

The solution would then be to first identify the location of the activated Sha Qi and then mitigate/weaken it's effect. 

As I have not seen your house nor do I know any of it's orientation and environmental changes, I could not help you further on this post. However, you could do a little bit study on your own to find out for yourself. It's not that complicated don't worry. 

Warm Regards,

JY