The person I contracted with is not the homeowner and has defaulted on payment, The home is owned by a sibling

Did the homeowner want the improvement? It is likely that the sibling acted as an agent of the owner, in which case the owner would still be responsible to pay for the work. If the work was completed recent enough for a mechanic's lien notice (ie, within 120 days), you may want to consider that route, assuming the other prerequisites for a mechanic's lien are met.

Good luck!