Now they've been released, here are links leading to the online demos of the Kotonoha sisters and Saki ^^
Akane : https://ah-soft.com/synth-v/kotonoha/demo/
Aoi : https://ah-soft.com/synth-v/kotonoha/demo/
Saki : https://ah-soft.com/synth-v/saki/demo/
Here's also the former ""demo"" of Saki (aka SynthV Web edition) : https://synthesizerv.com/web/
Akane : https://ah-soft.com/synth-v/kotonoha/demo/
Aoi : https://ah-soft.com/synth-v/kotonoha/demo/
Saki : https://ah-soft.com/synth-v/saki/demo/
Here's also the former ""demo"" of Saki (aka SynthV Web edition) : https://synthesizerv.com/web/