This can NOT happen, the risk is too big and people could get hurt. Your Mom has allowed this to escalate too far, too fast and can't see the danger she is inviting.

Your Mom isn't 'mad' but she is definitely being reckless and while trying to help someone else that she thinks needs her, she is forgetting about her family that need her. She doesn't know everything she needs to know to be sure this is a safe idea and she doesn't have the resources or ability to find out. Just getting to know someone over the internet is NOT enough and it IS possible to be deceived even when you think you know the person well. That's how online scammers work, they have to be convincing or people would not give them anything.

Even if they are telling the truth, the amount of help they're going to need and the long term commitment could be a disaster for you all. This person will be completely dependent on your family while in your country and they may have all kinds of complicated needs having come from a difficult home in a very different country, and with potential immigration questions. Offering to help someone with those kinds of needs is not a good thing to do if you are not truly in a position to offer that much help. Already your Mom can't even offer them a place to stay without making promises on someone else's behalf (yours), can she really offer what will likely be years and years of emotional, legal and financial support to a stranger without compromising her responsibilities to her family? When you speak to your mother about this, you need to remind her that YOU are her first responsibility and you are the one being put at risk most of all. You mentioned siblings, I'd be worried about them too. Are they minors? This is just such a bad idea.

You should speak to your father and find out if he is really okay with this like your Mom says? It sounds possible that like you, he didn't think it would do any harm for your mother to comfort this person online and now it's getting out of control and he doesn't want to upset her or doesn't know what she's promised them. If he really doesn't have any objections, then maybe there's other family members you can talk to? Most people outside this situation will think your Mom is making a bad decision and maybe you have an Aunt or Uncle that can talk to her. YOU are her first responsibility, because you are her child and family, this person online is not. It would be nice if it was possible for her to take care of the whole world, but it isn't, and if she tries to do that she might find herself unable to care for you and your family either because she gets scammed and loses your family's money, or because the person invited in to your home turns out to be more dangerous than expected or just requires more care than any of you can offer. It's not that they don't deserve care or help, it's that it's not help your family can reasonably and safely provide.

I hoped I would have good advice on how your mother could still help this person without the risk of being scammed or without going way too far like inviting them to live in your home but unfortunately I don't know any way that can be done. Though tragic, there is sadly a line where your personal responsibility for others ends. When caring for strangers involves risks to your own children that line has been crossed. Help offered to people in bad home situations, or in dangerous countries or in this case both, is complicated and difficult and full of risks even for professional organisations that try their best to do this, to take on this responsibility personally is very reckless and dangerous for your Mom, for you, for the rest of her family and even for her internet friend. Once he stays with you guys, what then? Can he work in your country? Can he legally immigrate there? What's his family going to do if they find out about you guys? How long can you support him? If he stays for some time and it doesn't work for any reason, where could they go? They'd be be alone in a foreign country with no where to stay? This isn't a real plan, it's a big, kind, but thoughtless gesture that needs to be reconsidered.