The Panchayati Raj system is a decentralized form of government in which each village is responsible for its own affairs. It was established to increase local governance and empower the rural population. Let's analyze the different bodies mentioned in the question to determine which ones exist at the village level:

1. Gram Sabha: This is an assembly of all the adults who live in a village and have the right to vote. It is the foundational body of the Panchayati Raj system, and plays a crucial role in the democratic process at the village level. The Gram Sabha is responsible for discussing and evaluating important community issues and developments.
2. Gram Panchayat: This is the executive body of the Gram Sabha and acts at the village level. It is responsible for the administration of the village and elected members from the local community run it. The Gram Panchayat performs tasks such as construction and maintenance of roads, public buildings, and sanitation, among others.
3. Nyaya Panchayat: This is a judicial body that resolves minor disputes at the village level. It handles small legal issues and allows villagers first recourse to justice without needing to go to the formal law courts. Although its role varies across different states in India, it is primarily considered part of the village-level governance structure.
4. Panchayat Samiti: This is a block-level institution within the Panchayati Raj system, and not a body present at the village level. It is responsible for coordinating the efforts of various Gram Panchayats within the block and dealing with planning and development activities that require economy of scale or shared needs among villages.

From the above analysis, it is clear that the bodies present at the village level are Gram Sabha, Gram Panchayat, and Nyaya Panchayat.

Therefore, the correct answer is: I, II and III.