Names for 'the other granny'.

ghastly mauve dress [gasp]

I am very fond of my DGD's other grandmother/DS's MIL/DDIL's mother

Petalmoore - it is not a Hebrew word but a Yiddish one and the word for the other granny is 'machatenista'. The word for the other grandparents (or just the in -laws) is 'machatenim'. We are best friends with my DiLs parents so this word is very good shorthand to explain who we are going out with. I believe that there is also a similar word in Greek.

If I was talking to somebody about the parents of my son in law(i.e. My daughters in laws) I would refer to them as my machatonim (Yiddish). It's a really useful word and is now used by my nonjewish friends too.

I think the Italians use the same name for each set of grandparents. NONNO for grandfather and NONNA for grandmother.

Perhaps we could invent a specific term to describe the relationship. I suggest Granny-in-law.

Not sure about adults but as children, we always called our father's mum Nan and our mother's mum Gran, easily noting the difference, we assumed that was the way that everyone did it. My own children have a Nan still living but not a Gran. I am Nan to my son's children and hope to be Gran to my daughters future children. Did anyone else do this?

Pamted. That is what we have always done. When I was growing up we only had one set of grandparents, so it was never a problem. They were Nan and Grandad.

My children had/have two sets of grandparents. My parents are Nan [ Nanny ] and grandad. Other grandparents are Gran and Grandad.
I am nanny to my grandchildren, and the other grandmother is nana.

Much easier for children to understand which grandparent you are talking about

It extends to the rest of the family too petalmoore
What to call DDIL'S or DSIL'S sister or brother and their OH, particularly if the OH are not a DH or DW? And any children, who are your DGC's cousins 'on the other side of the family' but not actually related to you.

It does get complicated, a word for those relationships would be nice.

I refer to my ex son in law's parents by their first names unless talking to my grandchildren when I call them Granddad and Grandma (their chosen names). I am Nan/Nannie/Nana - I have never asked what they call me in conversation between themselves but I know that they call me Nan in front of the children, and when I have spoken to 'Grandma' on the phone she calls me Dot and I call her Doreen. My husband died a long time before the grandchildren arrived so there is no confusion in using Granddad - although I think he would have chosen to be called Pops if he was here.

Well, I call them all by their first names as they do me when speaking to them, but it's when you are referring to them in conversation to someone who may not know them, eg we had a lovely meal with our 'daughter's husband's sister and her husband and children'
It's a bit long-winded.

I'm with Nina, Kitty and Anya when referring to DD's soon-to-be-ex outlaws! But NEVER in front of DG.

I spent most of my life in South Africa and Zambia and my Grandchildren call me Granny Africa and their other Granny, Granny Scotland

My mother in law was Danish and my own 4 year old granddaughter was highly amused when I told her if I had been Danish (as the mother of her father) I would have been famor (pronounced "fartmore" )

my son had an Italian girlfriend who lived in England, when they visited her parents in Italy the girls mother asked my son to call her "Mama seconda" perhaps the other grand-parent could be granny seconda

Why not Grandma..Christian name or Grandad .. Christian name? Easy peezy.

I agree with others, when speaking to grandchildren use the names thy call them, and to DiL 'your Mum' . However it would be useful to have a single word when speaking to other eg 'My grandchildrens othr grandparents' or my DiL s parents ar all a bit clumsy. Ive heard people call them 'the outlaws' and my sone often when speaking to us says things like - we;ve been to see the opposition. But I usually laugh and say : Aren't we all on the same side though?!
Our mutual grandparents is the best Ive come up with.

When our eldest daughter had our first grandchild, we sorted out which grandparents were grandma and grandpa, and which nanny and grandad, and luckily got our own preferences. However, as our other children added to the grandchildren, it got more complicated. We were already fixed as grandma and grandpa, but some other co-grandparents had already been named. Various solutions have emerged.
I once suggested to our grown up offspring that it would be a good idea for them to use our Christian names, but they were shocked at the idea, though their spouses do this.
So christmas cards have to be signed....Grandma and Grandpa/Dad and Mum and our Christian names.

I call my opposite granny my co-granny, but call her by her first name when speaking to DD and your mum when talking to Sil. The gcs call us Granny first name when talking about us.

The Danes have an easy solution. Mor = mother/Far = father so the 4 grandparents are:
mor's mor
mor's far
far's far
far's mor

That's a good idea so I suppose Mor's mor can refer to far's mor and people will know that she means her counterpart!
(is that right?)

When my DGS was born we were Nanny & Gramps, other GPs are Nanny & Grandad. Once DGS could talk he would always say NannyGamps to mean he was speaking about me/DH, since DH died I am simply Nanny or Nanny Grapes as I often buy his favourite black/red grapes from M & S. I don't often see them or need to refer to them as I moved 2 years ago & my friends don't know them.

All my step-Grandchildren called me Nanny + first name. My DM is Granny to both my DD & DGS.

My granddaughter is bi-lingual and in Bengali there are different names for paternal and maternal family members, e.g. maternal grandma is 'nanoo' paternal one is 'dadoo', same with uncles and aunts. Uncles and aunts also have different honorific depending if they are the oldest aunty, 'Borohalla', next one, 'medjahalla' etc.
I found this quite mind boggling at first but now slip into using all the different titles naturally, having said that I'm Granny Dee, it would confuse me to be called Dadoo. My granddaughter at 5 has no problem using each vernacular in the right context so now I'm working on Lancashire dialect!

We don't ever socialise with the opposite GP - not because we don't like each other but we don't have anything in common so we just call them by their names when talking to our DD & SIL but if talking to the GC its Nanna & Grandad

I've been trying to think Petalmore of how you could have phrased your question so more people really understood what you were getting at. Best I can do is, "Is there a general term for the off-spring's in-laws, especially when we all become grandparents?" For the latter, I tend to use co-grandparents but can't think of one for before we share grandchildren. Complications arise because my dil's mother is now on her 3rd husband. Thus, I suppose there are 2 step co-grandfathers & 2 step co-grandmothers.

Kittylester you must know my ex sil