hello.
As the title suggests, I want to check the number of followers of multiple channels (broadcasters) at the same time.
I know that other GET APIs allow you to continue adding parameters by treating them with &.
A number of endpoints support specifying multiple entities please refer to the documentation for the endpoints you are interested in to see if they do Reference | Twitch Developers
it was unclear you were being specific about followers information your question was written in a general way
Providing what?
if you have broadcaster (or moderator) authentication of the channels in question EventSub can be used to notify you of new followers and you can increase the total that way, then periodicially resync to account for unfollows/bot removals
Broadly speaking followers is a useless metric and doesn’t really tell you anything about the channel.
There are other metrics that might be of more use, but it depends on what you are trying to do/what your product does. Theres a bunch of possibilties that could be of use.