I wonder if they film it out of sequence. They showed Una a certificate possibly her grandparents marriage cert which clearly showed her grandfather was a confectioner, then later on in another context, Una asked the researcher if she knew what her grandfather's occupation was.
My guess is that her mother, being descended from Ebenezer Howard was probably living a middle class life and married "beneath" herself and was ashamed of her husband's family, hence Una never met them. Very odd that she never asked any questions though. I wonder if her father secretly visited his parents.