trying to plan summer vacations

So I am 5 weeks and 1 day today. I am due in late august early September and the only ones that know is myself and my husband. We don't want to tell anyone I the family until the first ultrasound and until the doctor says I am in the clear and good to tell others. HOWEVER my family is trying to plan flights and trips in JULY ! And it's difficult to keep it from them that I may not be able to fly then and won't be able to do any trips.