Matriarchs are usually crucial for interactions with bulls, they allow mating ect. and communicate to the bull when space is required. Putting two young cows in with a mature bull at their ages would also be quite stressful without a matriarchal presence. So whilst it can be done, it might not be in the best interests of the two young cows.Why would they have to wait getting a new bull? Indali is almost 8 and at the perfect age to get pregnant with her first baby. Which is badly needed now after this horrible loss.
Perhaps they allow Anjan to remain with the herd for a while longer before he moves elsewhere. He could give them the opportunity to learn how to interact with a bull which they'll have to learn themselves now without the guidance of Sundara.