If he says to his wife: O my mother or O my sister, or You are my mother or my sister
Question

What is the ruling if a man says to his wife, “O my mother”? Is this haraam or does it make his wife haraam to him?.
Praise be to Allah.If a man says to his wife you are my mother or my sister, or O my mother, then is it may be zihaar or it may not, depending on his intention, because the Prophet (peace and blessings of Allah be upon him) said: “Actions are but by intentions, and each man will have but that which he intended.” Agreed upon. 
In most cases a husband says such words as terms of endearment or respect, so it is not zihaar, and the wife does not become haraam for her husband thereby. 
Ibn Qudaamah (may Allah have mercy on him) said in al-Mughni (6/8): If he says: You are to me like my mother, intending zihaar thereby, then it is zihaar, according to most of the scholars. But if he intended to honour her and show respect, then it is not zihaar.  
The same applies if he says You are my mother or My wife is my mother. End quote.
 The Standing Committee was asked: Some people say to their wives: I am your brother and you are my sister. What is the ruling on that? 
They replied: If a man says to his wife: I am your brother and you are my sister, or You are my mother, or like my mother, or You are like my mother or my sister to me, if he intended thereby to say words of honour and respect, or he had no particular intention and it was not accompanied by anything that indicates zihaar, then this does not count as zihaar and he does not have to do anything. 
But if he intended zihaar by such words, or they were accompanied by something that indicates zihaar, such as saying these words when he was angry with her or he was threatening her, then it is zihaar and it is haraam. He has to repent and offer expiation before he touches her. The expiation is freeing a slave; if that is not possible then he must fast for two consecutive months; if he is not able to do that, then he must feed sixty poor persons. End quote from Fatawa al-Lajnah al-Daa’imah (20/274) 
Secondly: 
Some of the scholars regarded it as makrooh for a man to say to his wife: O my mother or O my sister, because of the report narrated by Abu Dawood (2210), according to which a man said to his wife, O my sister. The Messenger of Allah (peace and blessings of Allah be upon him) said: “Is she your sister?” and he disapproved of this and forbade it. The correct view is that it is not makrooh, and this hadeeth is not saheeh. It was classed as da’eef by al-Albaani in Da’eef Abi Dawood.  
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: Is it permissible for a man to say to his wife: O my sister or O my mother, intending only to express love thereby?  
He replied: 
Yes, it is permissible for him to say to her, O my sister or O my mother, and other such words which imply affection and love. Some of the scholars regarded it as makrooh for a man to address his wife in such terms, but there is no basis for that, because actions are but by intentions, and this man does not intend by calling her his sister that she should become haraam for him, rather his intention is to express his love for her, and everything that is a cause of love between spouses, on the part of the husband or of the wife, is something desirable. End quote. 
Fatawa Burnamaj Noor ‘ala al-Darb
And Allah knows best.