No.
We must have a minimum 20 players but can have as many as we like (I think) so in terms of 'spots' that is not true. What does happen is their salary is effectively removed from the cap and frees cap space. With that we can sign as many players as we like. Be it 1, 2 or 3 provided the combined salary is does not put us over the cap. Considering we are at the cap, it could not be more than what Durante and Stein earned combined (pro rata for games left). I also don't think Durant qualifies for the Australian marquee. Someone else mentioned that they had to be an Australian international within the last year or 2?? Shady on that detail, I am.