Have you read David Boutflour and Ann Eaton's statement? The answers to your questions are there.
Although I have read many documents connected with this crime, including those you refer to; I'm afraid I am one of those people that cannot trust what people say what they do or say what they did and I prefer to see what actions they actually took and their manner / mannerisms.
Nothing they said about going to the house and the discovery of the silencer should be believed IMO.
Not even your own
immediate family would go through personal possessions and property straight after a murder unless the police invited them to do so; let alone members of the extended family going through a house which they didn't own immediately after a bloodbath like this one. It certainly isn't British human nature.
IMO, that silencer was an object to be urgently retrieved from probably the normal place of keeping and at some stage, evidence collected upon it; then it was returned to be amazingly discovered.
The fact that they had access to the house indicates to me that they knew the house well, so did they have keys to be able to grab the silencer a day or so before it was found? Or (me being mischievous) was it already in their possession before the shootings?