The relationship between Thang Long and An Phu Gia in the Grand Sunlake project is established through Meeting Minutes No. 1004/2023 and related documents, including the construction contract, Agreement No. 135, and the exclusive distribution contract, under which An Phu Gia is the exclusive distributor while Thang Long is the project developer. However, pursuant to Article 23 of the Law on Real Estate Business, a project developer is prohibited from authorizing any organization or individual to sign deposit agreements, sale and purchase agreements, lease-purchase agreements, or transfer agreements for real estate formed in the future. Therefore, if Thang Long authorized An Phu Gia to sign such agreements or conduct transactions beyond the scope permitted by law, this conduct constitutes a violation of the Law on Real Estate Business. Any unlawful transactions carried out by An Phu Gia beyond its authority shall fall under the direct legal responsibility of Thang Long as the developer.