Could be an unpopular opinion but, I sort of got Charlie's point with the breastfeeding. There's was an episode when Charlie had told Theo off, and Theo ran straight to Shannon under the guise of wanting a feed. He also had expressed that Theo uses the boob as an excuse to avoid things, like tidying, bed time and other things.
He also pointed out the feeding seemed to be more for her comfort, than Theo. So I don't think its fair to say she wasn't supported, she was up to a certain extent. I think they also knew how over whelmed Shannon got, and the thought of her attempting to breast feed two, would be a melt down waiting to happen.
Maybe I just have a tainted view though, cause a family member breast feed a relative until he was FIVE, and used the same exact responses Shannon did. The relative use to wrangle that poor kid onto her breast, claiming he still wants comfort, and never wants to stop. His reaction said completely different.