This has the most ridiculous plot I have encountered in a very long time. The entire thing relies on the characters making a series of the most outlandishly ridiculous decisions you can possibly imagine.
There are many stories where you could point to a decision that was made early in the plot that if it was handled more realistically, none of the inevitable bad events would have ever happened, you accept this conceit because you can't have a story that ends on page 2 or halfway into the first episode.
This story however takes things to a new level, I won't include any spoilers but early on David Tenants' character deals with a bad situation in such a spectacularly bad way that it's difficult to comprehend. This character and his family then deal with the consequences of this spectacularly ill-thought-out decision with a series of decisions so outlandish they almost make the initial poor choice seem reasonable. It's not like they make a reasonable decision that goes bad or even make a poor choice it's like they sit down and try and think up the most effective way to make the situation worse and then do that.
You can have characters make bad decisions, you can have stupid characters make unintelligent decisions, and you can have insane characters make insane decisions but to have characters make decisions where there is only one very obvious terrible outcome is just lazy writing. To base an entire plot of a mini-series on a sequence of such decisions is just phoning it in.