1st form the LLC, and do an Operating Agreement that spells out who owns what, how ties are broken, how 1 of you buys out the other one, etc. etc.
2nd, assign or sell the rights to the existing businesses to the LLC. That's 2 documents, and may mean domain names, trademarks, trade secrets, good will, etc. A business lawyer can help document the transactions. A CPA can handle the tax aspects of this. If your lawyer also does IP, they can handle the acquisition of the trademark for the new company. Once you get this done, there will not be 3 companies, there will be just 1.
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