Is the testimony of a mother or daughter accepted when a husband claims his wife is his sister by suckling relationship (Rada'ah), and the wife denies it?

Primary text

If the husband claims his wife is his sister by suckling, and she denies it, the testimony of his mother or his daughter in his favor is not accepted. This ruling is based on the principle that the testimony of a parent for their child, or a child for their parent, is inadmissible. If the testimony comes from the wife's mother or daughter, it is accepted.