1. 'The tickets for the movie are already sold out' OR 'The tickets for the movie have already been sold out'
both are fine
The tickets for the movie have already been sold out usually has something that refers to the present.
I want to watch the movie but the tickets for the movie have already been sold out.
2. 'They accepted it as being of course"
What? I know only these
- They accepted it as being of worth
- They accepted it as being feasible
but I can't fit your example. Maybe other can help
of course is not, as far as I know, an adjective, course is a noun
maybe of course = OK or you meant off course
3. 'For me who am your friend...'
'For me who is your friend...' = For me the one who is
'For me who am your friend...' = For me as I am your friend
"For you who are" = for persons who are
"For you who are" = for you as you are
"For you who is" = for you the one who is
it is just how distant you want to be normally you-are me-am...
4. 'Spanish is my most difficult subject'
OK
5. 'none of the members was there when I arrived'
OK as well as "none of the members had been there when I arrived"
6. 'There is said to be plenty of whales near the coast'
maybe 'It is said to be plenty of whales near the coast" is better