How to open up about my Bi Sexual orientation? (27 yr old)?

If you are bisexual, you like the opposite sex as well. What’s the problem here? You don’t have to tell anyone about your feelings for same sex.

Why tell them at all?  Unless you decide to date a guy, and plan on bringing him home to the family. Only you know your family, will they accept you, throw you out, disown you? Why do you want to tell them, just to tell them?  

You must be comfortable with your sexuality b4 you start coming out. If you need more support call the LGBT ctr asap. If you think your folks will have a hard time contact PFLAG.org- a wonderful support group made up if mostly parents if LGBT kids. When you feel ready tell people one at a time. Add it into your normal conversation. The less emphasis you put on it the less crazy reaction you may expect Try it. 

Join some lgbt groups - maybe a coming out support group. Get allies. Learn how other did it. Read coming out story books. Understand current lgbt issues. Read up on the gay rights movement. There are also groups out their specifically for bi’s reach out to them too. You don’t have to invent the wheel for this. Just reach out.

The key is to have a network of supporters and to know the issues in advance. 

Then do it how ever you want. Tell everyone all together or separately or just out your self on Facebook.

A.  You don't NEED to tell anybody.  There's absolutely no reason to make a goal out of informing any of them.  Who cares if they know, or cares if they can accept it?  YOU shouldn't.

B.  Just stop making little accommodations to keep it hidden.  You have no reason to hide it, (even though it's none of their business, really).