How do you convince your parents to take out their investments?

Seems like they've let their emotions win over them when investing. Perhaps you can ask them their reasoning for entering into the position and what has changed since then. They'll have to see the light that either - they can grow their money in another potential counter / investment vehicle or that this investment is eroding their money and its going to be entirely wiped out soon.

If it is a listed company, get the company past 10years financial reports and study them. If they are bad, do advise your parents on it and have them exit it.

Try not to overpromise them that you can invest for a better return as older folks has a lower risk tolerance. You will need to understand their risk tolerance first too.

Perhaps you could get a professional financial advisor to speak to them?

I won't.

Harmony is more important than wealth. Who is to say that their value wouldn't change for the better immediately after you convinced them to pull their money out?

They will blame you. But if your investment makes a lot of money later, they won't thank you. (this applies to all our friends, colleague and life.... blames are easy, giving thanks is harder)

Unless the investment is part of some scam, or unethical stuff, leave it ba. Harmony is the most important for a family.