Step Daughter Visa to UK (from Australia)

Hi all, hoping somebody could help me understand my situation a little better.

I would like to bring my partner and her daughter to the UK from Australia.

• My partner (not married) has a daughter from her first marriage.

• Her daughter is 12 years old

• Daughter lived 50/50 with her mum and dad (week on / week off) until 18 months ago

• Father insisted daughter was to live with mum full time and he will see her for 7 weeks per year in the school holidays

• Father refused to sign sole parenting responsibility order until this week

• My partner now has legal sole parental responsibility of her daughter on court signed paper

• The court signed paper mentions being allowed to leave the state of New South Wales (australia) with daughter but doesn't mention international moves. The court consent order does give full parental right to the mother and none to the father though

• I am British born, lived in Australia for 8 years. My partner was born in Asia but has been an Australian citizen for over 10 years, her daughter is an Australian citizen

• My partner and I have a 2 year old baby

• We are looking to enter the UK mid next year. My partner would have had full parental responsibility for over a year by that point

Will I be able to get a visa for my step-daughter?

We exceed the financial requirements in regards to savings and salary.

Thanks

One further item to add: My residence in Australia was for 8 years on a temporary business visa. When this runs out I will need to return to the UK. My partner and I have a 2 year old son together. As I will have to leave Australia, is it worth mentioning this as some sort of mitigating factor?

Thanks