The last time the Followers of Set tried to conquer the world was over fifty years ago; a long time in some terms, but relatively short in the timescale of the long-running battle between the Followers and Those in Black. You have one main hope: that since their last attempt, during World War II, was so recent, they may not have recovered enough to be as much of a threat this time. You hope so; Those in Black certainly haven't fully recovered yet. You don't know all of who will be able to be here, but your best estimates are that it can't be more than a few dozen total.
Several of the scientists should have Dimensional Disruptors with them. These are the principal tools of Those in Black. The secret of their construction has been lost to the ages, but the principle is clear: they shut down dimensional ruptures, hard. Larger ruptures sometimes require several Disruptors at once, but none has been yet found that requires more than three Disruptors. Assuming everyone gets here, you should be able to close down whatever it is that the Followers are planning.
Personally, you like to have a more positive offense. You've armed yourself with a small one-shot flamethrower, a new development based on old Lemurian technology. The ancients would be appalled at seeing their tech used like this, but you have to be more practical. It'll only give you one chance, but it's a damned good backup to have when you need one. And who knows? With luck, things won't get violent...