I didn't really have to tell my mom, she just new something was wrong and guessed it but she wasn't upset or anything. I'm sure she was a little disappointed but now shes excited about it, its really kind of cute how she asks how her grandson is doing lol even though we have no idea what i'm having she's positive its a boy while i'm sure its a girl. The rest of my family was shocked needless to say but they've all accepted it also.
If you feel like you need the support of your bf then have him there with you, but if you think it might cause problems then maybe do it alone, but having the support behind you may make telling them easier. Its different with my situation. My family doesn't know the father yet, so its a little complicated. Good luck and remember it will be a shock for them so anticipate some anger but eventually they will calm down.