If the Trip owner of a Travel Together trip has decided to make the trip visible to your combined followers, they will receive just one notification whenever you publish a new step. So no worries about bombarding mutual followers with notifications of identical step updates.
Good to know: Followers receive the 'new step' notification about an hour after you create and publish the step, so your Trip group has some time to add their photos and videos too.
Whenever someone likes one of your steps, or if they leave a comment, you and all your Travel buddies will receive a notification.
Note that a Polarsteps user will only receive notifications if they have their notification permissions turned on in the app settings.
For more on notifications, be sure to check out this article: How can I turn my notifications on and off?