I don't think it was a matter of not putting Edith first - chronological order has nothing to do with how much the family care for Edith - it was practicality. I want to stick up for the Crawley family because I think a lot of people are just assuming that they don't care about Edith and think she's always being pushed to the background. That may have been the case in earlier series, and they may have overlooked her, but they have changed of late.
In S6E8, I felt like the family (remember, I'm excluding Mary) were always concerned about what Edith was going to do about her issue - most of the conversations between Cora, Robert and Rosamund were about Edith's tough decision and what to do. Tom shouted at Mary for the way she treated Edith. Violet's first question to Mary was to ask about why she hurt Edith, handling that matter before getting round to the Henry issue. And when Mary told Tom she had invited Henry up etc., Tom was quick to ask out how she planned to make it up to Edith.
Just because they are not chasing Edith or Bertie round the country doesn't mean they don't care, there are many explanations for passivity:
1). They can't force the situation - it's about Bertie coming to terms with the secret and having time. No on wants the family getting right up in his face, forcing him to make a fast decision (which may be the wrong one) and looking desperate. It may also give the wrong impression, look as though Edith's parents are desperate to have a Marquess in the family (actually, maybe that is the right impression...)
2). Edith and Bertie are adults - and they act maturely, can you expect to be interfering with the way your 30 year old daughter leads her life? The same daughter who has a child and a publication of her own? Unlikely.
3). Robert, Cora and Rosamund can't scold Mary - this is their fault, they put her on a pedestal for so long and now she's a grown woman so you end up wondering whether it's going to far to scold her. They should have but they probably think it's improper. Rosamund is Mary's aunt so you don't usually tell off other people's grown children. They weren't putting Mary ahead of Edith by not telling her off, they probably have to accept that she's out of thier control.
Tom is Mary's age and friend, Edith was the wronged party and Violet is the supreme head of the family that Mary truly holds in high regard - they could scold her.
I'm basically saying that we shouldn't be criticising all the members of the Crawley family for the terrible way in which a single member, Mary, acted. I also think we need to change our views of the rest of the family and how they treat Edith - it came slowly but they do care for her and I think they were very much concerned about her for the whole of episode 8.