Parents are responsible for the medical bills incurred for treatment to their minor children. If your son was under 18 at the time of treatment, the bill is yours to pay, no matter how you were spoken to by the party you wrote about.
Certainly I don't condone that person's conduct, if it was as you wrote. Deceptive practices and threats are not permitted in debt collection efforts.
If your son was an adult when treatment was given, point the collector in his direction or contact your son and give him the collector's contact information so that the problem becomes his and not yours.
The creditor apparently has a judgment, against either your husband or your son, and apparently has filed that judgment as a lien against your husband's interest in your home. In general, obtaining a "judgment lien" on real property is something a judgment credtor is allowed to do. Indeed, it's one of the reasons to get a judgment.
Simply yelling at the plaintiff's lawyer, or telling them they have the wrong person, is unlikely to do anything.
You should hire a lawyer to examine the following:
1. Did the creditor sue your husband, or your son? This can probably be answered from the complaint. If the creditor sued your husband, claiming he was liable for the debt, and got a judgment against him, then they had every right to file the lien (there may still be steps you can take, though).
2. If they did not sue your husband, but only your son, you will either need to convince them that they have placed a lien on the wrong property, or sue them to remove the cloud on your title.
3. It is not impossible that the creditor sued your husband, followed all court procedures, and got a default judgment without your husband ever seeing the complaint. It's very unusual, but it happens (more often, papers get served on a defendant, who ignores them, and then forgets he ever saw them). In any event, if they did sue your husband, you will want to take immediate steps to try to open the default and remove the lien.
Unless your plan is simply to pay the debt, you should talk to a lawyer without delay.