男朋友的家人

PS. I‘m from china,I can teach your Chinese.

男朋友的家人

我想跟他们见面。可是，我不会说中文。所以，我很担心。//我觉得这里，“怕”有点严重，用“担心（worry）”就可以。If you have a boss with bad temper, then you can say '怕' s/he. But here I recommend "担心".I guess your boy friend is Chinese? Then you boyfriends' family won't insult you or make you awkward even they don't like you haha. It‘s basic politeness to be nice to a guest. No need to be '怕'.But '担心' is suitable here. You '担心' they have a bad impression to you and thus don't support your relationship. 

我的男朋友家里有爸爸，妈妈，姐姐，和妹妹。Use '家里有' when you introduce a person's family stand, It's more natural.

我认识他妹妹，很可爱。我听说他爸爸人不错（？）。

short sentences looks too basic.Another example: ’I know him! He is handsome! ‘=我认识他，挺帅的。So a little homework for you:P

’You have met him yesterday, he is the tall boy with long hair.‘’你昨天见过他了。他是那个长头发高个子的男生。‘——Can you combine them into one sentence?

Also, you can use 蛮 replace 很 in south china in spoken Chinese. It would sounds really native.
我希望我能跟男朋友家人见面。