They're two out of 40 such sites for which the National Grid, their owner, wants to find partners to help in their development. The most recent story about them that I can find is
this one in the MEN from exactly 3 years ago. It suggested that residential use was most likely but it was unclear whether they'd be demolished or not. There have been residential developments in London that used the gasholder structure as part of the design but in other cases they've simply been demolished.
Back at the end of November 2019, it was stated that discussions were at an early stage. I can't find any later reports on what's happened in subsequent negotiations and, in particular, whether residential use remains the most likely prospect. Presumably talks about them have been and quite likely still are carrying on in the background.