Estate planning attorney.
Possibly a family law attorney (For a prenuptial agreement, but that agreement only governs you and your soon to be spouse. You appear to be looking for protection from 3rd parties, so you need an estate planning attorney).
However, unless one or both of you have "significant" net worth, the cost / benefit relative to the realistic chances of such an event are probably not worth doing the asset planning techniques that would actually help. But, you would need to sit down with an estate planning attorney to review your particulars.
You can protect them through a proper pre-nup agreement. You can also protect assests through a trust. An estate planning, wills and trust or family law lawyer should be able to help you.
This is a very complicated question.
Community property laws make any medical debt accrued while married, a debt of both spouses even if divorce occurs. So the best way to protect against this would be insurance.
As for debts other debts, it more or less works the same.
If you are concerned about pre-marriage debt of one spouse affecting the other, then do not commingle assets and get a pre-nuptial agreement.
This is not an issue you will likely get right by doing internet research.
You should hire an attorney who focuses on this kind of asset protection.
1845 S. Dobson Rd. Ste 201
Mesa, AZ 85202
We are a debt relief agency. We help people file for relief under the Bankruptcy Code.
If you live in Arizona, please contact me for actual advice; this is just speculation. It certainly is not legal advice. I don't have enough information to give actual legal advice. I can only take the limited information presented and provide a idea of what you might do and how it may turn out.