Astarion's only triggers if you get his approval up somewhat before learning he's a vampire (yeah I know what are the odds?)
Gale's seems really bugged -it took me 2 playthroughs without ever stumbling upon it, then I decided I'm not moving on with the next PC until I get it. From what I can tell (though there are some people who claim it can happen with higher approval) your approval with him shouldn't exceed "high" and the death quest should proc correctly + a lot of travelling using waypoints and camping.
Wyll's only happen if you take him to Windmill
