Brown v. Fullenweider
In Brown v. Fullenweider, 52 S.W.3d 169, 44 Tex. Sup. Ct. J. 553 (Tex. 2001), the Court held that an attorney could not sue to recover fees under an agreement incident to divorce, because the agreement in that case "merely allocated responsibility for any such fees as part of the division of their marital estate." 52 S.W.3d at 170.
Unlike Brown, the parties in this case did not simply list the obligation to Stine and then agree to allocate it along with any other assets and liabilities.
Rather, as previously discussed, the agreement specifically requires Stewart to use the net proceeds from the Lago Vista property sale, and then, if the Lago Vista property sale proceeds do not pay the debt, the Stewarts must each pay fifty percent of the remaining debt.
Notably, the Stewarts did not make similar promises to pay other third-party creditors listed in the agreement. Cf. Brown, 52 S.W.3d at 170 (because the agreement allocated responsibility for all the parties' obligations without distinction, no creditor could sue as a third-party beneficiary).