Saudi Arabian investor Prince Alwaleed bin Talal, who had initially opposed the buyout, also agreed to roll his $1.89 billion stake into the deal rather than cashing out, the filing showed.
The move comes as Musk's margin loan was reduced to $6.25 billion from $12.5 billion announced earlier, according to the filing.
Musk's $21 billion financing commitment was also revised to $27.25 billion.
Musk will continue to hold talks with existing shareholders of Twitter, including the company's former chief Jack Dorsey, to contribute shares to the proposed acquisition, the filing showed.
Qatar Holding and Dubai-based Vy Capital, also an investor in Musk's other venture The Boring Company, are also part of the investor group.
Reuters last week reported Musk was in talks with large investment firms and high net-worth individuals about taking on more financing for his Twitter acquisition and tying up less of his wealth in the deal.
Larry Ellison, a board member at Tesla and a self-described close friend of Elon Musk has committed $1 billion for the funding.
Twitter's shares were up about 2.9% at $50.5 before the bell, still below Musk's offer of $54.20.
(Reporting by Nivedita Balu in Bengaluru; Editing by Shounak Dasgupta)
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