Is Viola and Olivia both in love with Orsino?

Like most of Shakespeare’s heroines, Viola is a tremendously likable figure. She has no serious faults, and we can easily discount the peculiarity of her decision to dress as a man, since it sets the entire plot in motion. She is the character whose love seems the purest. The other characters’ passions are fickle: Orsino jumps from Olivia to Viola, Olivia jumps from Viola to Sebastian, and Sir Toby and Maria’s marriage seems more a matter of whim than an expression of deep and abiding passion. Only Viola seems to be truly, passionately in love as opposed to being self-indulgently lovesick. As she says to Orsino, describing herself and her love for him:

She pined in thought,

And with a green and yellow melancholy

She sat like patience on a monument,

Smiling at grief. Was not this love indeed?

(II.iv.111–114)

Not really, basically you have a love triangle. Orsino loves Olivia, Olivia loves Viola/Cessario and Viola loves Duke Orsino. (if you are referring to twelfth Night)