I am strongly leaning towards them being a species of Majano anemone, being that it’s insonesian live rock and based on what I can see in the photos. I spent about 15 minutes digging through the internet for alternative species that look similar and are from Indonesia, and Majano is the only one.
If you like them, you could watch them and see how they grow. Carefully monitor them. Update this thread in the future with more photos, etc. If they multiply quickly that won’t be good. But, if you’re planning on having a reef tank with corals and anything expensive or that could be harmed by a pest anemone running amok, just kill them now by taking the chunks off the rock they’re on, or with kalk paste, boiling limewater, Aiptasia X, etc.