I´d say let the Baktrians stay in India, and don´t give give Baktria to them. I know it´s a bit premature, but it´s not that long left until they were driven out south to India. Besdies, they look unlikely to be able to keep Baktria.
Just curious here, how are the Sauromatae doing? Just been a long time since you mentioned them, and they look like they might get into a conflict with the a lot of factions.