Did the Queen have guests onboard her boat, or was it strictly family.?

Yes Britannia was a floating Palace and she would entertain Dignitaries on Board I was disappointed when it was De Commisioned

It was great seeing her in Australia

Yes, very often. There was also a lot of international business deals conducted on board the Britannia, that was said to amount to billions of £s

They had guests from time to time, but it was mostly family.

If you are talking about the Royal Yacht Britannia, yes. HM regularly entertained onboard.

Royal orgies.