There are no lay member of the FSSPX, it is a society consistingly solely of priests. Pope Francis has said the priests of this fraternity may licitly celebrate nuptial Masses for those who desire them to. This actually means that any Masses celebrated by the priests of this fellowship are undoubtedly valid but also licit and that those who receive Holy Communion at those Masses do so licitly. He has also allowed local Ordinaries to permit FSSPX priests in certain circumstances to witness the exchange of marriage vows on behalf of the Catholic Church. FSSPX priests are also permitted by Pope Francis to hear confessions and absolve sins.
There is no comparison whatsoever between the FSSPX and the divorced and remarried. The Catholic Church has never demanded that those whose marriages have been witnessed by an FSSPX priest or bishop be remarried or required to be subject to 'sanatio in radice'.