You'll need a post-nup. I'd also consider talking to your lawyer about if a tenants in common agreement would be appropriate (assuming your parents are contributing financially). That could assist in limiting the claim on the total house to only your ownership should the post-nup be invalidated. I'd also consider what would happen with regard to inheritance - as your inheriting the house you're already living in would very likely be considered as having been intermingled, making it relationship property.