Does anyone else find this a bit creepy?

I find that odd but I know people who do it too. I only have one mam and dad. I call my MIL by her Christian name.

Up to them ....if it made them all happy what's to worry about
I wouldn't act like that, in fact both my son in law and daughter in law have always called me by my first name but everyone's different Anyway if they ve split up now it won't matter any more

I feel a bit sorry for Dave's mum

They were happy at that time so no, nothing creepy about it, I feel sorry for them thst it didn't work out

Sounds as if they were perhaps a bit over optimistic, but "creepy"? Why on earth would you think that?
Sad it didn't work out.

Not creepy but definitely 'jumping the gun'. Lack of restraint on their part but no real harm done.

It doesnt seem creepy to me, more a case of wishful thinking. Guess there is sadness now.

Yes, over-optimistic like one of DS's girl-friends who didn't last very long afterwards.

My sons in law call me by my first name which I consider normal but I had forgotten that I could never have called my MIL by her name but as she was German I called her Mutter which I don't like.
And never already after 4 months.

Are the GCs disappointed?

After 4 months?? Presumptuous of Natasha and of Dave's mum imho. Doesn't 'mum' have any little great GC of her own from Dave's DC, her actual GC? Natasha's DM must have iiis onthis too.
A friend of always referred to a much loved little boy as 'my step grandson'.

A friend of mine

*iiis was 'ideas'. ?

my daughters in laws always call her two children from her first marriage their grandchildren and treat them as if they were.I think its lovely that they love my two eldest grandkids this way and am happy they do

I can only assume that you live a very sheltered life if you think that's creepy.

Complicated perhaps. Many families are. Creepy? Nah.

Surely just because it's easier if you both refer to someone by the same name. Saying "your mum", "my mum" or "your gran" or "Natasha's GCs" is just too difficult, life's too short. My mum is "Nana" to my DCs and DGCs and from time to time I call her "Nana" as well. She also has a range of step GCs and GGCs who all call her Nana. We all know what the relationships are really but Nana is easy and she loves it.
Dave's mother sounds lovely, I hope Natasha keeps in contact with her.

It took my daughters partner 5 years to call me by my name, it was always your nan, your mum, we all turned round in shock, it was so funny.

One of D's ex boyfriends used to call me Mother. I quiet liked it, they were only teens at the time. Her ex husband and new partner both use my first name.
I never knew what to call MiL so it was 'your mum' 'your dad' I was never brave enough to ask her opinion.
Nothing creepy about op as others say just wishful thinking.

To each his own. What we personally find 'strange'!! is normal to another.

Nothing creepy about it just wishful thinking for a future that didn't turn out as expected I myself wouldn't do it or have my son and daughters partners call me mum you only have one mum

It sounds like they were desperate to make a new family unit unfortunately society puts such store still on "normal" families that people often a desperate to fit in and not feel excluded. I was a lone parent when my children were growing up and I know how left out they felt when visiting happy 2 parent households I also found my social life took a nose dive too when I became a single parent!.
Personally I would be reluctant to bring a full on family approach to a new relationship especially if there are children around as they particularly need stability!
My own SIL's all call me by my first name and I would not want to be called mum by them as I am not their mother and they have their own parents!

Sounds like a case of their hopes and expectations not matching up to reality. Some desperation there? Wouldn't call it "creepy", though.. Just rather sad now I've heard the outcome..

Each to their own!

I don't want to be called Mum by anyone but my own children. Hiwever i am known as Nana by grandchildren and stepgrandchildren as it's too confusing for them all to call me different names.