Praise be to Allah.
According to what was said in the question, this is a weird group whose ideas, beliefs and conduct are misguided. It is strange that you say they have strict rules, but they are so lenient with regard to other peoples property and overstep the limits by using peoples things without their permission. This is Zulm (wrongdoing, oppression), and Allaah says (interpretation of the meaning):
The way (of blame) is only against those who oppress men and rebel in the earth without justification; for such there will be a painful torment [al-Shooraa 42:42]
The Prophet (peace and blessings of Allaah be upon him) said: The whole Muslim is sacred to another Muslim: his blood, his property and his honour(Narrated by Muslim, 4650). And he (peace and blessings of Allaah be upon him) said: It is not permissible for a man to take any of his brothers property except with his agreement (narrated by Imaam Ahmad, 20180).
The Creator and Lord of wealth is the One Who has forbidden the violation of the wealth which He has bestowed on people in this world and given them permission to possess it. So how can these people accept this corrupt justification for going against the rulings of Allaah? The fact that their deviation is extreme is abundantly clear from the fact that they do not touch or speak to anyone who is not a member of their group. I wonder how they can live among people if they are not even allowed to look at others!
Moreover, they have forbidden looking at the heavens and earth and finding out what Allaah has created in them, by forbidding scientific research and finding answers to questions about natural phenomena. But Allaah says (interpretation of the meanings):
Say: Travel in the land and see how (Allaah) originated the creation, and then Allaah will bring forth the creation of the Hereafter (i.e. resurrection after death). Verily, Allaah is Able to do all things [al-Ankaboot 28:20]
Say: Behold all that is in the heavens and the earth [Yoonus 10:101]
Do they not look at the camels, how they are created? And at the heaven, how it is raised? And at the mountains, how they are rooted (and fixed firm)? And at the earth, how it is outspread? [al-Ghaashiyah 88:17-20]
And there are other texts which indicate that we should ponder the universe and find out about what Allaah has created.
Ideas such as those promoted by these people do not find acceptance except in an ignorant society and among foolish and simple-minded people who do not know the basics of Islam. We have to advise this misguided group and call them to the truth, whilst warning people against their falsehood. May Allaah protect us and you from confusion, innovation and misguidance. And Allaah is the Guide to the Straight path.