First, those three sims were in "rabbit hole" professions. In my case Science, Criminal and Culinary.
Second, non of their co-workers were celebs, so I was able to limit their socialization to just co-workers. I made a Business profession sim as well and one of his co-workers was a single star. He gained a single star of celebrity status as a consequence. But I ignored the agent calls and anything else that might increase my status. If the constant phone ringing annoys you, turn off the ringer on the phone or even go into game options and shut off the opportunities. This is a nice and necessary option EA added to this edition. I used it in the Business sims case. It cut off opportunities, but hey, more challenge, right? He was a still a single star when he reached level 10 and owned the world.
Obviously, you won't be able to avoid it if your sim is in a profession requiring celebrity status.
I limited my sims outings, including group outings to dive bars and avoided contact with stars, intervening if necessary. I turned down ALL party invitations. There did not seem to be any consequence for doing so other than the second phone call later saying they missed my sim at the party.
I normally play with free-will turned to the half way point. That way my darlings still take care of routine things like peeing, cleaning up after themselves etc; but they don't go running off after a star if they spot one from the balcony of their apartment.
Last, sometimes celeb status is unavoidable in Bridgeport. Bridgeport is meant to be a hotspot, happenin' place. It is crawling with celebs. There may actually be more celebrities and vampires than regular sims. It's part of Bridgeport life. If you live there, you deal with it.
I made a sim with the Chess Master LTW. I knew up front he was going to have to interact with celebs and just accepted it as part of the challenge of playing him. He turned out to be my most enjoyable sim. When he reached his LTW, I said to myself, "What the heck..." and ran him the rest of the way up to five stars. All without answering a single agent call.
I do not play Legacies. I also do not generally play families. I usually just run a single sim through to a lifetime wish, a career path or some sort of challenge I have set for myself.
If I did play legacies and families, I would adapt the attitude I did with my chess player: Accept the inevitable and deal. Treat it like an additional challenge.
Do what the celebs in real life do. Pursue very visual, open public lives in the pursuit of the sim's careers and goal. Then sequester your sims off in their private lives (pursuing skills, child rearing etc.) Treat the paparazzi as part of the background, like the wind, the wall or that fountain over there. Don't talk to them or interact with them, just let them flash away their petty lives. If my celeb sim gets a scandal, I laugh and let it slide. I treat the negative moodlet as an added challenge for the time it last. But you can sue or pass it along to some other sim if it tickles you. The main thing is just treat it as part of the game challenge and move on.
I deal with vampires the same way, btw. But I won't go into them here because this is a celebrity thread.
Hopefully this gives you enough detail. If not ask for more specifically or PM me.
Enjoy!