Fermatas with tremolo, trills and multi-note tremolos

Here is the result with Sample Modeling Strings :

-Tremolos work perfectly
-Trills work perfectly
-Multi-note tremolos are not working great due to the length of notes shortening the fermatas while the actual notes are still playing.

Is there a specific reason why you used 3 slashes on the first tremolo but 4 slashes on second?

No, not really, I just tested this at some point to see if it would make a difference but the problem is the same, it is the half notes causing the problems since the Fermatas will refer to the first half note to generate the tempo changes without taking into account the rest of the bar.

It’s a work in progress, I just want to report my findings with my setup.

I’ve noticed that behavior yesterday with multinote tremolo. What you can do is select the fermata and modify its properties. If you enable “Hold only” it should solve the issue. [But it doesn’t. Sorry for this, you are right, there’s some refining to do there. The fermata does not last the time it should last, the whole bar.]

I don’t think I’ve yet found a library where multinote tremolos always work perfectly – never mind the added complication of a fermata. The safest thing to do is to create a secondary hidden staff where you write the passage out in longhand and disable the playback on the notated version. This way you have full control.