It can be that at the end non of these players will leave the club because if you check they don't have a back up striker and they're not making any effort of getting a new striker which is something they need. Manchester United are some how getting things right when it comes to how well they play and this striking department is where they had problems last season and they shouldn't go back to that time when scoring goals was the problem, now Benjamin Šeško is in the squad but they need back up before the window closes. If Amorim really sees these players Zirkzee and Hojlund as important players I don't think he'd let either of them to go and it seems the lucky one to stay will be Zirkzee.
Although it is possible that one of them could leave, the situation is now becoming increasingly unlikely, as the summer transfer window is about to close, making it more likely that they will remain at United, even if their role is limited to being substitutes and part of the rotation. However, they could still get some opportunities, though this also depends on their performance.
Currently, Hojlund and Zirkzee have failed at Manchester United, as their progress at Manchester United and their previous clubs shows a significant difference.
Loaning them out could be an option, but if Amorim wants to keep them for at least one more season, it is still very much possible.
I think the right decision would be letting Rasmus Hojlund go and meet his master at Bayern Leverkusen since ETH is also considering coming for him. Zirkzee can remain in the bench and substitute for sesco. Manchester United has been unlucky lately with signing players. All their supposed world class players signed under ETH all flopped at Manchester United. Antony has rejuvenated at Real Betis but not back to the starting lineup. Hojlund has been very bad and cannot bench second in anyway. Instead of leaving all these players, why not sell them and get more money to strengthen the back? Martinez is injury prone, Leny Yoro is getting over laboured. I think the team really need to offload players and Hojlund is the best option to go.