The issues between AnuSar will probably stem from him having always felt second best in their marriage (what happens when you marry someone without their full consent and they stay with you mostly to make a 3rd party happy.... indeed Kalyani was way too involved in their relationship as a match-maker since day 1, so when she believed to be no more, even AnuSar's relationship died ), especially if Anu has no issue with KalMa being pretty involved in their sister's live while Anu takes a backseat.
Actually, the think is, though that Anu has never dealt with small aged kids as a mother.
Kallu fell in her lap at almost 18 and without either one wanting it and they somehow adjusted to it and then grew close, but she has no idea how to be a wife and mother because she never experienced those in the age women normally do, and now that she's getting them... maybe she simply has no interest and/or doesn't know how to fit into the new role.
Kalyani, though her daughter, has had more of a friend-like relationship with Anu and vice-versa, having to deal with a 4/5 yo is a whole different thing, and probably more in Kallu's comfort zone than Anu's.