P55

Can anyone help? I am a little unclear on who has to fill in the 47A form. My partner has Australian citizenship and we have been together for 10 years, I have three sons from a previous marriage who all live in Australia one is now a citizen, one has permanent residency (both married to Aussies) and the third is on a four-year visa sponsored by an Australian company with PR after this. Do they have to complete the form as they are already in Australia? Also, my partners, two children are in the UK and have no intention of migrating. None of the children is dependent on us. Would they have to complete the form?