This is obviously a personal view based on your perception of the risk presented.
Maybe due to working in London and being more accustomed to seeing armed police on the streets, and being vigilant I don't share your view. While the events of Manchester and Westminster are obviously still fresh, statistically being exposed to terrorism is a rare occurrence.
I recall that after the 7/7 attacks, London carried on as before. While we had people from Leeds and elsewhere refusing to come to London shortly afterwards due to their perception of the risk, overlooking the fact that we were still at our desks in London.
On my last visit to new York there were troops on the streets and at the subway stations but this didn't stop me from enjoying the visit and getting around New York as you would normally. In fact it was rather reassuring which was probably the main point of deploying them.
I know it can come across as being blase and I don't want to belittle your valid concerns, but I work on the principle that if your times up, its up and there is no point worrying about what may or may not happen.
If the FA Cup final on Saturday is shown around the world and there are large areas of empty seats as people have decided to stay away due to their perception of the risk, does this mean that the terrorists have won?
Whatever your wide and brother in law decide to do, I hope that they can enjoy the game and that you can relax anf not worry about their safety.
I work in Mayfair, and am VERY accustomed to seeing armed police and uniformed military guarding St James's Palace so it's nothing to do with that.
I just feel that what if this was a cell as they fear and that Manchester was a dry run for something bigger in a stadium/venue?
I accept that we can't change our lives for every little thing that happens and was back on the tube post 7/7 the next day but my response was brought about by the perception that the critical threat level is always used after this sort of scenario when it isn't.
They clearly have very credible intelligence that this definitely wasn't a one off loan wolf scenario and that shouldn't be taken lightly.
Yes I accept the odds of being killed in a terrorism related incident are infinitesimally small versus being say run over crossing the road but to take this situation lightly is in my opinion fool hardy.
Whilst I don't want the perpetrators to have 'won' it's a sobering time to be living in and any allegorical references to WWII are missing the point. There we were dealing with a known threat, a common enemy who weren't hiding in the shadows and it was abundantly clear what the risks were so the only way of dealing with that was to go about your business in a stoic stiff upper lipped manner.
Here the enemy could be anyone, the attack won't be heralded by the sound of an air raid siren and it will be aiming for maximum collateral damage.
Sometimes right, sometimes wrong but ALWAYS certain