This is very troubling. What would motivate the SSPX to suppress Lefebvre's sermons? Is it because the sermons were "too extreme"? Could it be that the sermons were too elementary that they would make Lefebvre appear unlearned? (I have heard it said Lefebvre's sermons were not very profound) -- A friend made an observation to me: whereas the SSPX tries to suppress anything of their founder that would be unfavorable to the Vatican or the general public, the TFP has not tried to hide anything about its founder, Prof. Plinio Correa de Oliveira. His "sermons" and articles are readily available on the Internet (TIA Website being one of many) in several languages, even without disclaimers.
At any rate, Fr. Schoonbroodt is correct to make the sermons available to the public, whatsoever be their content.
I think Fr. Schoonbroodt should upload the sermons to a Website where it won't be at risk of being taken down. I imagine Matthew would know some good resources here.
My understanding of copyright as someone who lives in the United States is: you can upload whatever you like onto the Internet, even copyrighted material, as long as you don't profit from it monetarily and post a "Fair Use" disclaimer. If Fr. Schoonbroodt sent the files to an American and had an American upload it, perhaps that would resolve the problem.
Unfortunately, Fair Use as a defense to copywrite infringement in the US is a bit more complicated than that:
Not only do Fair Use laws and precedent vary from state to state, but depending on the locale of the plaintiff and defendant, the case would likely end up in federal court (ie., in cases where both parties are from different states, or countries, venue is usually the federal courts).
Moreover, there are a whole string of factors judges assess in determining whether the use of copywrited material is “fair” (eg., is it transformational; what percent of the material has been reproduced; it the use commercial or educational; etc).
Here is a good article which discusses:
https://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/Normally, the judge plays a balancing game: If more factors are in favor of the plaintiff, an infringement action has a good chance of prevailing, and vice-versa. But even in such cases, the outcome will not be certain.
If an infringement suit is brought, a defendant will need to show more criteria in his favor than the plaintiff can.
As regards the use of unauthorized copywrited material, one would be well advised to perform an assessment of Fair Use criteria in advance (better still, gain the permission of the copywrite holder, or failing that, seek the legal advice of a copywrite attorney).
An entirely separate defense against infringement actions in some cases are SLAPP laws (SLAPP is an acronym for “Strategic Lawsuits Against Public Participation”).
SLAPP laws are designed to combat plaintiffs from stifling public conversation by threatening or instituting lawsuits asameans of intimidating opponents into silence, in matters of public interest.
Which is all to say that if anyone was considering publicly publishing materials for which the SSPX has already demonstrated a resolve to litigate (not only in this matter, but also against Avrille a few years ago), they had better get a lawyer.
It would be a very stupid (and expensive) move.
NB: I am not an attorney, and this is not legal advice.