@8w_gremlin Yes, the t-rex breaks the grapple by virtue of size. This demon has Truesight, which I mentioned in an earlier post was not affected by illusions, which the cloak generates.
And for Bloodaxe, the poison dmg was 26 on each attack. A failed save w/ your resistance makes it 13 poison dmg. A successful save w/ resistance makes it 6 dmg.
So success/failed save total damage for Bloodaxe would be:
Attk 1: 28/35
Attk 2: 29/36