They formed a business partnership; how should the profits be shared among them?

The partnership that has been established among you is
called, in fiqhi terminology, mudaarabah; it is a partnership in which the
money (capital) comes from one party and the work is done by another party,
whether the party is one person or more than one person. The profits are
shared among the partners according to what has been agreed upon among them,
on condition that the profit or share agreed upon is a specific percentage
of the profit, such as half, one quarter and so on. 

It says in a statement of the Sharee‘ah Standards Council: 

1.

It is stipulated with regard to profits that the manner in
which they are distributed should be known in a manner that rules out there
being any unknown factors and prevents disputes arising; that should be on
the basis of a known share of the profits, not on the basis of a set amount
of money or a certain percentage of the capital. 

2.

The agreement on the shares of profits must be made at the
time of drawing up the partnership contract. It is also permissible for both
parties to change the amount of the shares at any time, with the consent of
both, so long as the period to which this agreement applies is stated
clearly. 

3.

If neither party said anything about the shares of profits,
if there is a custom to refer to with regard to this distribution, then it
must be followed, such as if the custom is that the profit is to be shared
between them equally. If there is no such custom, then the mudaarabah
partnership is rendered invalid, and the active partner may take a wage like
that of his peers for the work that he has done. End quote. 

Based on that, the basic principle is that if each partner’s
share of the profits is known from the beginning of the partnership between
them, that agreement should be followed. 

If there was no such agreement or stipulation of shares of
the profits, then reference must be made to custom. The cases of
partnerships similar to yours should be examined to see how much each party
took, then that should be applied to your partnership. 

If there is no such custom that you can follow, then this
partnership becomes invalid, and you three are entitled to a payment from
that investor (i.e., payment that is deserved by someone who does work like
that which you did) in return for the work that you have done. 

And Allah knows best.