Is it permissible to share an internet service with neighbors without knowing how they will use it, given that I and some committed individuals need it for religious matters, and there are reckless people among them?

It is forbidden to participate in anything that leads to a forbidden act, because it involves aiding in sins, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Therefore, you should only participate with those whom you trust in their uprightness and that they will not use the internet in ways displeasing to Allah.