Unexpected close relatives- a conundrum

[Petros]

Having compiled an extensive tree and identified all my (small) number of first and second cousins I have been surprised to see two close relatives, apparently  a 2nd (339 cM) and a  3rd cousin (167 cM), found by AncestryDNA.

Both are shared matches with my 2nd cousin once removed (145 cM) linked via my grandfather's elder brother. The two unexpected relatives appear to be from the same family, the 3rd cousins mother sharing the 2nd cousins surname.

On these figures are they more likely to be related via my grandfather, who  did desert my grandmother, or my great grandfather?

She has yet to reply to a message while he said he knows little of family history but has 28 1st cousins

[Craclyn]

Put the number of cM into the Shared cM tool to see the possible relationships with their probabilities:
https://dnapainter.com/tools/sharedcmv4

[Gadget]

... and attempt to create a tree with the possible relationships

Add - I had  similar matches 18 months ago and was able to find my maternal great grandfather by contacting 2 of them and  extensive paper trails

[medpat]

I found a distant cousin on my DNA site so wrote to her welcoming her into my paternal line as she'd connected to all five of us who were linked to my 3rd gt grandparents. She wrote back saying she didn't understand. I went into detail of all five of us and were we connected to my 3rd gt grandparents via some of their 8 children. She wrote back saying she was new to DNA and didn't understand what I had written. I looked at her site and she stated she was from the USA with mid European ancestry from both parents. Mother's line was easy to find a paper trail but she was having difficulty with father's paper trail so took a DNA test.

I reread my email to her and found it very easy to see she was related via my paternal family but decided to leave it. Six months later she wrote asking for help. A good friend of her's turned out to be a half sister, they found a half brother but he said he didn't want to find out about his true father but all three were bewildered about who it could be. Then a cousin from the same state as the others appeared on the DNA site (all connected to me) and she said her grandparents had divorced and he'd gone to live in their area of the state - he was from the UK. The lady was shocked at his name as she knew him as a great friend of her parents and was in her 20s when he died.

The lady sent me his name to research him - his mother Mary's maiden name was my paternal surname, found Mary's father John was already on my tree but I hadn't yet found a marriage and family for him. John was the grandson of my 3rd gt grandparents. I sent her all my information so now she's coming to terms with having a family from Dudley instead of mid Europe.

DNA may alter a lot of paper trails

[Petros]

Thanks all

The tool suggested by Craclyn is very useful, and supports my current theory of the less closely related of the two.  The most likely suggestion for the former that is reasonable is a half cousin, since my grandfather lived from 1882-1964, the other suggestions are highly implausible.

[Craclyn]

Glad you are making progress with where they fit in.