I say build your own wealth.
If your parents' business is a sound one, they should be able to pay off the business's debt with the business's cash flows. If they can't do that, why throw good money after bad?
If you put money into your parent's business, that muddies the waters. Does that mean you'd have an ownership stake, since you are putting in capital? Is that just a gift to them? What if they don't leave it to you -- what if someone makes them an offer they can't refuse? What do you see out of that deal? It's a reasonable expectation to inherit, but there's no guarantee.
If you secure your own future, you will be in a position of strength to help later. Secure your own breathing mask before helping another family member with theirs.
Also, with a Roth IRA, you can take out the contributions at any time, penalty free. This makes for easy access to money you can reallocate in an emergency.