Is a partnership valid if two individuals agree to rent out their specific animals for a fixed rent to carry a certain load?

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If two individuals rent out their specific animals for a known rent to carry a specific load, the partnership is invalid. Each partner is entitled only to the rent for his own animal. This is because the liability for carrying the load is not established upon their responsibility. Rather, the hirer is entitled to the utility of the animal he hired, evidenced by the fact that the lease is terminated upon the death of the animal hired. Furthermore, the partnership is not established upon a guarantee in their liability, nor is it established upon their personal labor for which wages are due. The partnership also implicitly involves agency, and agency in this specific manner is invalid, similar to one saying, 'Rent your slave, and the rent shall be between you and me,' which is invalid, just as saying, 'Sell your slave, and the price shall be between us,' is invalid.