EUSS FAmily Permit For non eu mother in law

I am a Sri Lankan national married to an Italian citizen and we've both got settled status in the UK.
I'm about to apply for an euss family permit for my mother and I have read that dependency is already assumed.
However during the application process they do say that you can upload proof of financial dependency.
I've got financial proof of my husband sending money to my mother however the money was sent from 'Italy' to Sri lanka , would that be a problem? Or would it best not to upload any ?
And lastly I've got a sibling who's under 18 will she be able to apply as a dependent of my mother/husband?
As I have read as of 2017 only the parents in law can apply for family permits.
Would truly appreciate it someone could get back to me and thank you so much.