Joint Ownership of Real Estate and Lawsuit

Name of State: New Hampshire
My wife and I own a home with her sister and boyfriend. They have been together 20 years, but are not married. He is in bad debt to the tune of at least $50,000 and recently he received a summons to appear in court from 2 of Citibank's credit card companies because he owes a total of $10,000+ and has not made any payments for at least 3 months.
My wife and I and her sister are not in debt and have great credit histories. My question is, will this lawsuit against him endanger our ownership of the house? Can the credit card companies who are suing him come after our home, even though it is jointly owned? If he eventually goes bankrupt, will this have an affect on our joint ownership, too? Thanks for any info.

They eventually can file a lien against the home as to his portion of the equity, and they may be able to prevent any sale etc. until the judgment is paid off--if they win the case.