Yes its legal, even if you are a corporation. Corporations do it all the time. Well, not so much lately, but surely you remember all those IPOs that were done back in the internet boom.
There are lots of regulations around doing an IPO or a secondary offering. Both state and federal. Not something you would want to attempt without good legal help.
You can create a "syndication" on a smaller scale. I'm part of such a deal. The syndicator found a property (a mini-storage), created a company, got a bunch of us to buy "units" in the LLC, got a loan and bought the property. Its now operating, and pays out distributions occasionally. Whether it turns out to be a good investment or not remains to be seen.
The trick is that he did not solicit for funds. All of the investors are people he knows. He's built up a list of investors over time, based on a lot of personal contacts. He's done a number of this sort of deals. So, when he has a new one, he lets all of us know he has something coming.
Its perfectly legal to form an LLC and sell units in that LLC to anyone. The limitations come around advertising for investors. You will want to know and apply all the relevant state and federal regulations for such solicitations. Again, a good lawyer is what you want.
I disagree with this premise, though:
I think there is a huge market for group investors(people with bad credit or unable to come up with a down payment.)
People who are unable to come up with a down payment have nothing to contribute to such a deal. People with bad credit are unlikely participants. Folks with bad credit tend to not have much cash, either. Otherwise, they wouldn't have their credit troubles.
You're looking for people with money. People who will buy into your deal, and give you the money you need to make the investment. Real estate investing is about investing -- MONEY! Nothing else. All these other approaches -- birddogging, wholesaling, fix and flips, developing, etc., are legitimate businesses that involve real estate. But they aren't real estate investing.
Maybe I'm missing something. How do you see people with bad credit and no cash being able to contributed to a company?