AFAIK absence allowance is 8 months for first 24 months. Then 8 months for the next 36 months. You can get waivers for personal/professional reasons but they want you to provide documents that prove you actually needed to be abroad. If they are not satisfied, they might refuse to extend your residency. How strict they are is unknown to me. Lawyers said this depends on the person who’s reviewing your case. I tried to learn more details but couldn’t.
I am guessing they wouldn’t be ok with you spending 6 consecutive months in PT and the rest abroad with your aged parents just because you want to spend quality time with them? Especially if you want to do that for 5 years.