My Grandfather the elusive Charles Duff

[Girl Guide]

It seems like we are all leaning towards Charles George Duff as being the right man.  Trouble is is actually proving it.

How about seeing if you can get the Court Support Order as suggested by Sandblown?  The application may need to be done via your mother rather than yourself.  Try, you have nothing to lose and if you get it, great 

[Kiltaglassan]

I don't know what a BEF is

British Expeditionary Force 

[sparrett]

I don't know what a BEF is

British Expeditionary Force 

Oh! Of course. What a dill

[Jool]

Apparently his wife Jean was disabled and couldn't have children.. Hence the offer to take my mum on?

As already mentioned by Heywood, Charles George Duff had a younger sister called Jean. 
In 1939 his sister Jean was noted as incapacitated.

I agree there may have been some confusion in Carl's family over Jean's relationship to Charles.

[MonicaL]

With everything that has been found so far, a couple of further ideas to consider for research is to request a copy of Charles George's service papers from WW2 www.gov.uk/get-copy-military-service-records/apply-for-someone-elses-records 

Confirmed here by others is CG's birth date and death details which all help in finding someone's service records.

The cost is £30 and will likely take months to get, but maybe worth considering to see what his service history was and compare with the info you have been given?

Also, from names found, there looks to be a quite a few family trees on Ancestry for this family group. Don't know if you have a subs to a/try. If so, you could consider messaging tree owners to check whether any have done any DNA research to let you compare to your mum's? You mention that there is already a possible DNA connection with Alice, daughter of Gideon Duff from the family contact you have found. There are others on a/try connected to the other siblings for Charles.

Monica

[heywood]

Do you have to be related though to obtain Army records?

[Girl Guide]

Not necessarily:-

You can apply for a copy of someone else’s service records if any of the following apply:

you’re their immediate next of kin, for example their spouse or parent
you’ve got consent from their immediate next of kin
you have a general research interest - you’ll only have access to limited information, unless they died more than 25 years ago
You need to know the person’s full name, date of birth and service number.

[heywood]

Thanks 

I only knew the first two.

[Meelystar]

What an interesting thread!
Just a further comment, you do not need a service number to obtain military records. I got my Great Grandfathers a couple of years ago and did not have that information. I just provided his full name, date of birth and death certificate.