Is my theory re Norwegian grandfather via DNA correct?

[rkive82]

I am R born 1952 in England.
My twin brother D is a DNA match with shared 45 - 52% 2530 cM. No mystery there.

Our mother H was born in Norway in September 1924. Her mother (our grandmother) W born 1893 spent her whole life in Trondheim. On the birth certificate for H, the mother was W (we have no doubts about that), but the father was said to be AO. I have yet to find any DNA matches with the family of AO among hundreds offered by Anc***** and MyHer*****.
 
The next closest DNA match to me is K born 1966 in Norway. We have 5% shared DNA 316 cM across 16 segments. Ancestry suggests K, D and I can be "Half 1st Cousins." I have identified the mother of K to be M and the grandfather of K to be JHON and the great grandfather of K to be OJON. There are many cousins on Anc** and MyHer** who are shared matches.
So cousin K and I have the same grandfather JHON but different grandmothers.
I hope you can follow all this. Is my theory sound?
Richard

[brigidmac]

That sounds like the most likely scenario

[Biggles50]

Sounds like a reasonable hypothesis.

I would suggest building a small tree with all those quoted and with some of the shared matches included. 

Export a Gedcom and import it into DNA Painters WATO tool.

The analysis will give you probability options