Advice needed!

Katie
We haven't told out families yet that we are expecting. I work almost every weekend and SO works Monday to Friday. We finally have a weekend off in a few weeks and invited everyone to our place for a BBQ for the big news. His sister just told us she invited two of her friends (I've never met them). Is it completely unreasonable to ask her to uninvited them? I don't feel comfortable sharing the news with complete strangers there.