Capacitated multiple vehicle routing problem with handovers
These problems are studied but with different terminology such as drop-off. See below and references therein.

The Finite Capacity Dial-A-Ride Problem,
M. Charikar and B. Raghavachari,
in Proceedings of the 39th Annual IEEE Conference on Foundations of Computer Science (1998)

Algorithms for Capacitated Vehicle Routing
M. Charikar, S. Khuller and B. Raghavachari,
in Proceedings of the 30th Annual ACM Symposium on Theory of Computing (1998).

Dial a Ride from k-forest
ACM Transactions on Algorithms, 6(2):2010
Anupam Gupta, MohammadTaghi Hajiaghayi, Viswanath Nagarajan, and R. Ravi