The group of relatives assembled for the weekend in question is well chosen, from a plot perspective, with very diverse characters and attitudes, albeit that there are not so many family members that we lose track on the respective opinions and motives. In spite of the a priori agreement on the whole process, we observe that some are getting cold feet and we see them wanting to postpone or even dismiss the whole procedure. Reasons for it vary but are certainly genuine and we can follow their trains of thought very well. These withdrawals happen with one after the other, each with different motives, and each eventually coming along and prepared to stick to the original plan. It sounds confusing but the script is well designed and the timing is perfect.
One example, to illustrate the sort of objections, is that one daughter regrets that she did not spend enough time with her mother in the past, having given more thought to her career and other priorities elsewhere. Now that she has more time on her hands, she welcomes the opportunity to renew the relationship with her mother, and to discuss matters of mutual interest. This is something that I can understand fully, as having similar ideas myself over having not spent sufficient time with my parents, in spite of them devoting ample time to me when I was young. A second argument of the daughter is that doctors can be wrong in their predictions, in other words that the planned euthanasia is much too soon, and that medicine can be invented in the meantime to prolong her life for many years to come. All this is just an example of aforementioned turns of events, everything just rational and understandable, yet endangering the plans that were so well thought through.
It is an achievement in itself that it all happened on screen within 97 minutes, in a limited time span in which not a second was wasted, letting events pass by in a logical order and evenly spread over time. Don't assume an overall gloomy atmosphere, since there is ample humor included in spite of the circumstances.