But why would Eurus try to kill her siblings, and Watson, at this point? We later see all the elaborate things she planned at the Sherrinford prison and the Holmes family home, which needed all three of them alive.
There was no guarantee that all of them would survive the explosion. It's actually kind of lucky that they all end up standing near an "exit", e.g. Eurus couldn't have predicted that Watson would move towards the window furthest away from him.
And the flat is one floor above ground, so jumping out the window is dangerous even without an explosion behind you.
Maybe the grenade's purpose wasn't to kill them, but to motivate them to come to the prison. But if Eurus just wanted to make sure that the three would pay her a visit, sending them a grenade seems unnecessarily risky (also, if Mycroft knew for sure that the prison had been compromised, there is a chance that he would bring an armed security force with him to take back control).
- Did Eurus try to kill Sherlock, Watson and Mycroft with the grenade?
- If not, then what was the purpose of the grenade?