Hey Big Team! Assuming you were in charge of casting these characters (who would soon make surprise appearances in the MCU), and you had your pick of current talent...
She-Hulk (must also appear as Jennifer Walters)
Monica Rambeau
Mary Jane Watson (as 17-19 yrs)
Namor
Tigra (must also appear as Greer Grant Nelson)
Sentry
Overwhelming, I know. Here are my picks.
She-Hulk/Jennifer Walters -- Abigail Spencer; she would rock as Attorney Jennifer Walters and play a fitting younger cousin to Mark Ruffalo
Monica Rambeau -- Tyra Colar; I read Monica and hear Tyra. If you hold their pictures side by side, she IS Monica Rambeau.
Mary Jane Watson -- I literally have no idea. Zero. Zilch. I have agonized and I still can't imagine who would own this role.
Namor -- Jason Behr could bring an angry Atlantian Prince to wreak havoc on the surface world.
Tigra/Greer Grant Nelson -- Michele Dawson, for off the chain athleticism, acting chops, and hypnotic eyes. Bam!
Sentry -- Stephen Amell; He plays Arrow, but he was born to play Sentry. The psychological layers, the agony, the tone, the looks. No doubt in my mind.
Have fun casting!