I am going to visit some family abroad.
I'm assuming you're an adult and have the freedom to make your own decisions about this. If you're an adult, and you want to go visit your extended family, you have every right to do so. If you're a teenager, and you're living with your mother, you don't have quite as much freedom to do what YOU want to do and perhaps may wait until you're older and do have the freedom to make choices.
I had similar issues with my late mother.
First of all, I am an adult, not a teenager.
Has your mother met these relatives, and if so, when was the last time that she saw them? When was the last time that she contacted them and asked how they were doing?
These relatives are in Australia.
While it would be polite for the relatives to ask about your mom once in a while, for her
From what I am reading, you were the one who decided to reach out to these relatives after the dealth of your father...and that these relatives really had no contact with anyone in your immediate family for 25 years before that time.
Insanity: doing the same thing over and over again and expecting different results.
. -Albert Einstein