Lookout, I see both Sheila and Colin as being too selfish to consider anyone but themselves and it was only latterly, after Sheila became too ill to cope that Colin started to act responsibly. I'm not saying they didn't love the twins but I feel they were used like pawns in a game of chess. It must have destroyed June, who may have ached to have her own babies, to see her grandchildren pushed from pillar to post.
Oh yes,April,,the whole lot of the adults were selfish so far as I see,,with no exceptions. With some,,it's a bad idea to have children during the " partying stage " of a relationship,,as responsibility just isn't there at all,,and as you said,,those boys saw a lot of different faces looking after them during their short years.
June wouldn't have taken too kindly at all to this " way of life " which was becoming more regular than she'd hoped for, within the family,,and would indeed have been worn down and at the end of her tether,herself.
I wonder how June did get her black eye that time ?.It's something that Jeremy would know,I'm sure because of working at the farm and seeing his mum regularly. Do we know how long this incident came,before the tragedy ?