Overall is the SSPX growing or shrinking? I believe it is growing, albeit slowly.
It's growing because of the # of children born to parents and also due to the admittance of novus ordoites. The problem is that the sspx has taken the view of "quantity over quality" for the last 2 decades. They admit anyone who "wants the latin mass" and do not have strict standards for newbies, who never learn the total depth of V2's problems. Thus, the sspx now is full of "conservative (former) novus ordoites" and many lukewarm sspx'ers. All the staunch anti-V2'ers have left (and most of the anti-V2 priests have been kicked out).
Yes, it's growing, but it's not moving in the right direction, so it's growth is irrelevant.
Is the SSPX fragmenting? Is there a uber liberal faction of the SSPX that wants to split away from the conservative faction? The SSPX has always had small breakaway groups. I've nothing against the resistance breaking away, if they are worried about a potential deal with Rome, but they should acknowledge that no deal was done by Fellay. Until a deal actually happens and the terms and conditions are understood and the SSPX has clearly made an unacceptable compromise, then I am left wondering what exactly is being resisted?
The sspx is analogously in the period between 1962 and 1969, when thinking of the interim period between the Traditional Mass and the introduction of the novus ordo. So many changes/experimentations happened during these 7 years that the Faith of the people was changed even before the new mass was unveiled.
The sspx has adopted a policy of interacting with roman officials, diocean bishops and diocesan priests on a grand scale, and on a weekly/daily basis. Just as roman officials were "friendly" with modernists/protestants and had "concelebrations" with heretics in the 60s, so the sspx has made "friends" with the novus ordo both in theory and in practice. Once a "deal is made", the change and subversion of the sspx will have already been accomplished.
The resistance (and the sspv groups) are just like the Traditionals of the 60s and 70s - they see the writing on the wall long before the sun has set. This is not to chastise those who react "as it happens" (some people don't have the gift of anticipating or 'reading the tea leaves') but many times (as history has shown) the reactionaries are way too late, and unprepared for the chaos, whereas the visionaries were prepared to fight the battle and survive, since they saw the fight coming.
The calls and the doom from 2013/14/15 have not panned out.
They absolutely have. The sspx leaders (and their modernist friends) just changed tactics (but not their course) and have decided to be patient. The frog will still be boiled, but just not as quickly.
My experience of Resistance members' families in the UK is that they are smaller than the average SSPX member taken as a mean, modal or median average. I know of a couple of big families but I know of lots of small families and unmarried people and people who were shacked up and fornicating in their 20s and 30s and came back to the SSPX when their Halcyon days were over and now I believe are over-compensating. You see this frequently with reverts and converts like they are trying to make up for lost time.
The resistance is mainly measured by its priests and bishops, and their principles. The Traditional laity (of any group) can hardly encompass an accurate measure of the group's worth. (This is even true of Catholicism pre-V2. The "fewness of the saved" means that the majority of Catholics are horrible examples of Christ's Truth.)