Question: Why don't they even think of pretending the victim just drunkenly tripped in the kitchen while getting a sandwich, and his sister-in-law reflexively tried to catch him, unfortunately holding a knife? He thought he would live a few more minutes, so he could have backed up the story. Instead, everybody (victim and police) just takes it as given that the stabbing will reveal their relationship.
Question: Is it practical to have a shack with a living tree growing through it? I imagine the roots would eventually disturb the floor, and rain would get in at the 'exit hole'. A storm may also move the tree so much that it damages the roof. Additionally, does the tree get enough water with the ground around it covered?
Question: When Richard reminisces about England, he talks about going to the pub and having a pint. Yet the whole time he's in Saint Marie, he is never seen to drink alcohol with the rest of the team; only cups of tea. Why?
Answer: Most likely they had only tropical exotic drinks, he wanted an old fashioned English beer.
Question: Why did the cord on the wall phone in the police station change from straight in the early episodes to coiled later?
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
As long as such changes aren't an obvious continuity mistake (e.g. changing multiple times during a day), one can just assume the change happened in-universe as well. Things do get broken or updated occasionally. It adds a bit of realism, in my opinion.
Answer: In Texas, I've seen trees grow through fences. Uproot concrete sidewalk slabs. On another website, I saw a picture of a bicycle that had been chained to a tree and forgotten. Twenty years later, the tree grew around it, enclosing it in the tree trunk.