What a fascinating story! Yes, I think we have a link. The clincher is one Gilbert Pitcairn Selwyn Shand born in 1890 - the name Pitcairn is too good to be true! I plan to get back to you in some depth eventually - I am now in contact with a cousin who is a descendant of the Shand/Simons couple. There's a lot to discuss, but the Merthyr Tydfil connection also helps - the Simons line comes from there.
More as and when I know more......
Graham