For the past 4 years, I've had 100% custody of children, aged 4 and 6. No family court orders. Ex walked out of mediation. He sees children every few months and lives within 2 km. He will not allow a surname change to mine. I would therefore like to add my surname to their current name, i.e. double barrel. He will also not allow this. My legal question is: can we do this? What is the process for a name change please? Thanks.