Can’t speak with regard to how IFTTT manages multiple users, or with regard to what applets are available within the USA, to compare and contrast that to those outside, because I only use those outside.
In the past, when I started using IFTTT, their native geolocation was a little unreliable, so I use Life360, and it works perfectly. Create an account with Life360, set up locations and family members as you require, and then link it to IFTTT. Build your own applets as to whether it is one or all members you need to arrive or leave for a given location, based on your needs, and change the chosen Blink system status accordingly.
For this, mine is simple. An IFTTT applet for when I leave my chosen Life360 location to arm the system, and an applet for when I arrive at my Life360 location to disarm the Blink system. Could not work better and has never failed.
As far as what’s available for Blink. If you have ‘do something on motion’, which is available for the IF, and you have ‘Arm’ or ‘Disarm’ option for the THEN, I don’t think there’s much else that is needed. In each case the other half of the expression is handled by the other service.
For example, my siren looks like this.
If motion detected from camera: ‘Inside cabin’, then turn on eWeLink single channel smart switch: ‘Cabin siren switch’.
The switch then routes power to the siren. I have inching set on that switch for 60 seconds (means it reverts to previous switch state after a set amount time), so the siren goes off again. If they continue to hang around, and set off Blink again, then it will sound again, and so on. Since this camera is inside, I haven’t had a single false alert, not even from a spider, or similar, and it always sounds on testing. Fortunately, I’ve also had no real alerts. When the applet does trigger, the IFTTT app receives a notification, so I know the siren has sounded. That way I will get the video(s) from Blink, and be advised that the applet ran from IFTTT, so I will know the siren sounded.
Unfortunately it is not an XT2, so I can’t enable early notifications, so the siren sounds after the Blink activity has finished, because the push notification from Blink doesn’t go out to IFTTT until the activity has ended. With an XT2 it could be speeded up a little. Still, it’s good enough, because they would expect to be entirely undisturbed, if they were breaking in here, and wouldn’t be rushing, so the siren sounding whilst they are in there is good enough for me. At least it will come as a shock to them and they will be alerted to the fact that someone likely knows they are there.
You don’t have to have the IFTTT app on your phone, but I chose to have it so I could get notifications of the applets running.