How we used to live Hi Karrie,
I watched the How We Used To Live series you mentioned which was set in 1936-1953 and one of the girls was Avril as you said. The other children were Jimmy, Patricia and Edward.
How We Used To Live 1936-1953 is on YouTube and I hope someone will add the other series. My favourite is the How We Used To Live 1954-1970 series which also featured Jimmy and Avril (who both had their own children by then), together with Michael Brady (who was a boy in the later episodes of the 1902-1926 series), his wife and their children, as well as Michael's Uncle Albert and Auntie Bertha. Jimmy and Avril's brother Edward re-appears halfway though the series.
As mentioned on an earlier post, Avril and her husband Laurence are indeed killed in a later episode when their mini is hit by a multicoloured Volkswagen van on the motorway. Strangely, despite Jimmy, Avril and Edward being in ther series, their parents were never mentioned and it seems they had died off screen as they didn't come to Avril's funeral - and not one mention of them was made when Avril and Laurence were killed, or when Edward married the Brady's older daughter.