The clue is in the name. Only their acquired independence from Corbyn truly unites them — otherwise, what is there? It is true that all seven are, to greater or lesser degrees, pro-Remain and in favour of a second referendum. But that disposition scarcely distinguishes them in a House of Commons already sizeably (by about two-thirds) pro-Remain: it is therefore a scant selling point. Why not join the Lib Dems, if that is your chief opposition to Corbyn?