I was thinking that may be Jack as well. It is possible he moved back and forth on troop ships. If you check this site, you will find Jean's birth, Ivy's marriage, and there is a marriage for a Jean Tute and a James Medcalf in 1951, perhaps she did move back homehttp://www.freebmd.org.uk/
The message boards are all the same, no matter which site you are on. However, you might post a request on the county board for where they lived in England.
It is hard to find Ivy in the US without knowing more about Jack., because the last available census records are from 1940.
You can order their marriage record, which should at least list father's names.