Locus, maybe.
https://github.com/Myzel394/locus
It looks like you need to build it yourself if you're using iOS.
You can Nextcloud hosting from a reputed provider like Hetzner. install the maps plugin and you'll be able to share location with users. Since you'll be the admin, you can make as many accounts as you want.
I think you can share your location with signal
Signal supports a single momentary position, but not live location.
I don't know how much my privacy is actually being respected but I do go for the "use as many different services as possible so no company knows absolutely everything about me." Approach.
I have a Garmin watch. I press a button on it twice, and within a minute or so a group of people I selected recieve an email with a live link, that shows my path and current location. Once I press the button again my live location ends but the list of people can still see my whole "activity". I think that expires on 24 hours but I'm not sure on that.
It's use is supposedly to show off exercising? I use it when I'm out hunting public land and might be wandering away from my truck or driving to several nearby trailheads in a day and don't want to have to remember to tell my other half "I know I said I was going to Fish Lake but so got distracted and stopped at Deer mountain and then drove to Owlfield but I parked on the south side of the trailhead but ended up walking north 3 miles..."
Companies do share data either directly or indirectly, so I don't think your approach of spreading it out is as effective as you think it is. Still not the worst thing to do in addition to other measures though. Another thing is to use a unique email address for each site to make that one common data point no longer common.
Yep I do the email thing. And yeah, I know they all share everything, but at least I make them work for it.
life360
This is definitely the wrong answer for this community, but may be an acceptable answer for this post. I have never used it nor would I ever recommend using it, but the conversations I have had with others who do use it make it seem like the service is far better than any alternative. Given the OP's requirements and willingness to both pay and sacrifice privacy, it seems like this may be appropriate for OP.
I would still explore other options though. There are several competitors to Life360 and presumably there are some with better privacy policies (even if the service would not typically be recommended on this community). Maybe OP could use a service like https://tosdr.org or https://tldrlegal.com to better evaluate those options that would likely not get much attention on this community.
Depending on the required features, maybe the Live Location Sharing feature of chat apps like Element may be sufficient. It could also help improve the privacy of the users' by switching to a more private/secure messaging app in the process.
My go-to will be simply to use a maps app and then share it over messages (Signal, etc...)
I'm afraid your best bet here will be using WhatsApp.
Edit:
FindMy (for Android) might also be usable for that, but honestly if you just want it to work I'd still vouch for WhatsApp.
Glympse is a possible app I've used for this in the past. You set a time in the app that you'd want to share for, and others can either view in an app - else they can watch via a unique web link on any platform.
ulogger client is not cross platform (android,fdroid) for the logger but it can logg to any webserver you are in control of to ulogger-server : https://github.com/bfabiszewski/ulogger-server
Privacy has become a very important issue in modern society, with companies and governments constantly abusing their power, more and more people are waking up to the importance of digital privacy.
In this community everyone is welcome to post links and discuss topics related to privacy.
much thanks to @gary_host_laptop for the logo design :)