Getting your immediate family ready for a vacation can be hard work. Opening the invitation to extended family might seem like a better idea when it's originally brought up than when the arrangements are actually being made. Even if you are the person making the majority of the plans, there are ways to simplify the task so that everyone can remain happy.
Decide on the destination for your vacation and choose the dates you will be traveling.
Verify the means by which you will be traveling.
Extend the invitation to family members and inform them of the dates you'll be traveling. That way, they can make their own decision and you can still go where you want to.
If they accept your invitation, start looking for accommodations. Some hotels will let you block rooms in advance. Each family can call and pay individually.
Make plane reservations if needed. Inform the rest of your party of the times you'll be arriving and departing.
Reserve a car if needed. Remember that it might be cheaper to rent larger vehicles and split the costs rather than smaller vehicles for each individual family.
Enjoy your trip!