Children moving to the uk with Belgium national mother

Hi. My mother is Belgium national. She is also disabled registered in Belgium and gets full disability allowance.

She wants move to the UK. With children 18 years old 19 years old and 21 years old children whom are not Belgium national but Belgium residents and dependent and living with her.

My question is. Can the children come with her by car and ferry from Calais without uk visa. And ask the border force to issue them visas at the border under EU free movement law. If they prove they are her children with birth certificate and other letters.

Is it possible that they will allow them to enter the UK with her?

Thanks.