Help! Hubby And Best Friend Have Same Name = Major Confusion/disrepect!

My husband and his best friend happen to have the same first and middle name. When the best friend came to live with us I called the best friend by his First and LAST name to seperate them. As an Amerian,  I found that to be just too long and difficult to do everyday all day so I just call him by his last name to shorten it.

Their schoolmates call them Tunde1 and Tunde2 - but even that is confusing depending on who they knew first and considered to be #1.

Anyways, The best friend is married now and his mother in law lives with him. My hubby and I are relocating and have been living with his best friend for a short time.

The problem is that this woman keeps telling me it is disrespectful to call her son-in-law by his name. (My husband is fine with it). I feel like its none of her business because I have known him longer than her and he NOR my husband have ever had any issues with what I call him. In  fact, my whole family calls the best friend by his last name - to also separate the two.

Since I am a guest - I have tried to call him  the nick-name that the mother-in-law suggested, but I can never remember and the name is stupid (she gave him the nickname based on how he ate some stew she made back when she first met him) and I have been calling this guy by his last name for many, many, many years now.

Well, his mother-in-law (I guess she is very traditional) Just sees me as rude, and disrespectful to him in his house, and she keeps picking on me now for every little thing I do.

I am not trying to have strife with this woman (afterall, she's not MY mother-in-law), and she is now pitting the Wife (her daughter) against me - by complaining to her all the time an saying stuff like "Don't let this woman enter your house and disrespect you and your husband." etc.

I told my husband and he says to ignore her, but it is hard because I am often in the house alone with her, and we have to live with them a little while longer until our own home is ready.

ANY ADVICE on what to DO?