Herbie, Heather's father, was like an unofficial 'uncle' (or in Colin's words, 'third grandfather') to the twins. The relationship between Colin and Heather was stable. I'm baffled by that part of the interview, but maybe he was just being nice to Sheila's memory and trying to avoid leaving people with the impression she was 'alone'. Thinking about it, Sheila was in quite a sad situation.
This man, to me, seems like somebody with a double personality: I'm betting he's a completely different person in private to how he comes across in public interviews, in which he is the shy-ish, artsy 'nice guy' from Cornwall with multi-coloured glasses. He's like a mirror image of Jeremy: an actor essentially, not a transparent person. Jeremy, I think, hid a vulnerable core behind brash self-confidence; Colin, I intuit, is very much the opposite, somebody who hides a much more strident personality behind a benign, slightly stumbling persona. I wonder what he was like with Sheila in private?