Thanks Jeff for telling me about Eric Roberts who died in Bangor in 2000
I've been to the Archives again and drawn a complete blank but these are the records I looked at:-
Llandudno Parish Baptism record 1894 to 1908 no trace
" " " " 1917 to 1933 no trace
St Mary's Church in Trefriw Marriage Register no trace
Now there are a number of reasons why I have had no luck tracing Robert and Elizabeth such as they never lived in Llandudno during their marriage or the children were Baptised in a Chapel and those records are unfortunately not available.
The births of the children were registered in the Conway Registration District but that District covers many towns, villages and Parishes but unless you have any address it's like looking for a needle in a haystack and at the moment there is nothing more I can do to help.
You have obviously done lots of research on the family and you are hoping to find living relatives of the Roberts family. From what you have said already I assume that the family has more connection with Gwynedd than Conwy. What I would do if I was you would be to concentrate on Eric R J Roberts and you might get some clues from the newspapers at the time.
The newspapers would be the North Wales Chronicle based in Bangor, the North Wales edition of the Daily Post or possibly the North Wales Weekly News
The Crematorium at Bangor have been very helpful to me in the past when I've been searching for graves in that area and the link to their website is
https://www.gwynedd.llyw.cymru/en/Residents/Births-marriages-deaths/Deaths-cemeteries-crematorium/Crematorium-and-cemeteries.aspxThe Archive dealing with that area is the Gwynedd Archives in Caernarfon but if you come up with an address in the Conwy area then please post it on here.