One wonders how exactly this is proposed to work.
There is normally one management company for a block. What precisely gets managed may vary, but typically includes the external maintenance and common parts of the block (i.e. those parts under joint ownership by all residents, such as the gardens). Now if part of the group gets the maintenance on their bit done one way yet another group does something else, how does that work? What happens to external painting, for example.
I think you'd better ask the breakaway group of residents what exactly they are proposing and why upfront money is needed anyway. What for? - maintenance is paid for as one goes along.
I'm surprised CAB can't help - this sounds like a legal issue, around how the residents are set-up constitutionally for determining how maintenance is undertaken.