In western culture these second/third wives are referred as aunties and mostly called by first names, while in Chinese culture it's inappropriate to call first name directly, especially from the next generations. it is also very difficult to reflect the order/family status if calling by aunt/auntie+name, and the order is a big deal in Chinese family culture.

Mama is universal and easily understood. In this specific context it's important to be creative and include some special reference to reflect the Chinese culture. I would suggest using "Da mama" (大妈） "Er mama" （二娘）"San/Si/Wu mama"（三/四/五姨） ...etc. to address the first/second wives, while using Mom/mother only to refer the biological mother. Da/Er can be regarded as titles which also reflects the order and a short explanation on the Chinese meaning can be annotated. The use of Mama also embeds a sense of formality and respect so I believe this is a great creative solution.

in a family where people have close relationships who get along very well, the greetings can use casual names as (casual name)+ mama, for example, 如果名字叫 翠花 可以叫 Hua mama， 玉兰叫 Lan mama, 以此类推.

如果是提及某个小妈，翻译为 my father's second/third wife.

如果是在人物与这些妈的对话中，需要address她们，这里有一个网页可以参考一下：

https://dadfixeseverything.com/nicknames-for-stepmom/#:~:tex...

71 Lovely Nicknames to Call Your Stepmom

这里是针对继母，而不是二妈，三妈的，但是总有一两个可以借用的。

Offshoots of ‘Mom’ and ‘Mommy’ that you could use for your stepmom include:

Ma
Mama
Mumsy
Mammy
Momzie
Mother Hen
Mamadukes
Big Momma
Mummers
Mothership
Moo Moo
Momster



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Note added at 14 hrs (2023-06-14 01:07:41 GMT)
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为每一个小妈/大娘安排一个这样的称谓，在全书中固定下来一致地使用。

正室（大妈）: principal wife, chief wife
二娘: secondary wife

A man could have a chief wife, lesser wives, and concubines in ancient times. For your reference only.

Reference: https://en.wikipedia.org/wiki/Concubinage