Regarding fellow welcoming individual to stay (6)
I believe the answer is:
remain
'to stay' is the definition.
('remain' can be a synonym of 'stay')
'regarding fellow welcoming individual' is the wordplay.
'regarding' becomes 're' ('re' means regarding or about).
'fellow' becomes 'man' (fellow can mean a man).
'welcoming' indicates putting letters inside (in sense of 'inviting in').
'individual' becomes 'i' (Roman numeral for one, ie individual).
'man' placed around 'i' is 'main'.
're'+'main'='REMAIN'
(Other definitions for remain that I've seen before include "Don't leave (the EU?)" , "Survive" , "Stay (in a place)" , "Stay behind" , "Stay (in position)" .)