It is far from ideal, but with Perraud and Livramento out injured the options are limited unless a loanee comes in to cover Livramento until the New Year.
Why do you think that is 'clearly' what the club want to do with them? I think it looks like the plan may be for them both to start in the 1st league game.
We play formations that use two strikers, that really needs at least four strikers in the squad for decent depth. So neither Adams or Armstrong need to leave.
Their local paper claims it was...
'In the region of £30m'
https://www.watfordobserver.co.uk/sport/17825048.watford-announced-signing-ismaila-sarr-rennes/
This is an interesting read...
https://www.dailymail.co.uk/sport/football/article-11045531/Southampton-reaping-benefits-hiring-Joe-Shields-head-senior-recruitment.html