The FCP B team is set as a separate team to the main club, (you can select to manage them at game setup) so you can't ask for extra staff slots/wages unless you are the manager of the team (which is why the drop downs are grayed out, take over as FCP B manager and you can use them) - the options can't be 'enabled' because they are a separate squad.
You CAN take control of hiring and firing for the b team via the 'staff ' on the sidebar and then 'responsibilities - staff' and scroll down there's a 'recruit staff (FC Porto B)' option which you can 'take control' by pressing the button.
You can then search for staff for the b team by entering the staff search, clicking 'edit search' and then changing the 'include' drop down so only staff interested in the b-team are shown (for example Jari Litmanen can be hired for the FCP B team as a coach from game start).
So, you must put yourself in charge of hiring and firing for the b team before they can search and hire staff. Hope this was helpful.