They will not work with the Belkin Powerline adapters.
You should be able to use the old hub with the Powerline adapters, otherwise you may be better gettina a proper wireless access point like the TP Link WA701ND.
Other options on this page.
Do you know if it is possible to configure a Home Hub 4 to act as a wireless repeater to a Home Hub 5, without connecting them via ethernet or powerline adapters?
No, its not possible.
BT have a repeater http://www.shop.bt.com/products/bt-dual-band-wi-fi-extender-600-9WW6.html