It's interesting because when they first started and only just had Reu, they were seemingly happy. There is no question in my mind that Houston and Halo were unplanned, but the attitude towards them was different. With Houston, it was a surprise but one more child didn't seem too bad for them and I think they worked out how they would adapt and cope. When Ella became pregnant with Halo, they had previously indicated they were done and weren't having any more children, particularly due to the toll it was having on Ella. Considering this, Halo probably was the biggest surprise and biggest 'accident' and I don't feel Ella has bonded as well with her as she did when the other children were babies. Or, at least, they aren't putting in as much one on one or quality time with her as opposed to what we have seen with Reu and Houston as babies.
I also think the reality of having seven kids did not sink in for a long time but now they are really starting to feel the pinch and stress of it all.