OK firstly, consideration doesn't have to be "valuable". It has to have _nonzero_ value, but that value can famously be as trivial as "a mere peppercorn" [0]. Furthermore: "a peppercorn does not cease to be good consideration if it is established that the promisee does not like pepper and will throw away the corn".

[0] https://en.wikipedia.org/wiki/Peppercorn_(legal)

The point is that the law doesn't attempt to make everyone "be nice", nor does it protect you from making a bad business decision. It's really just ensuring that there was _some_ business (ie, some exchange of nonzero value) occurring at all.

Secondly, it's important to note that a written contract is not absolutely needed to enact shared ownership; a written contract (or a deed, or a shareholder's agreement) is just to formalize the agreement in writing to avoid disagreement later.

If you start working together, shared ownership is the _default_ in the absence of any mode-changing agreements. Were they working together? A recorded video, in which they take turns looking into the camera and effectively saying "We are working together" [1] is a pretty strong evidence that, at one point, they were working together.

[1] https://m.youtube.com/watch?v=_P6oXe1YI90

Thirdly, in the absence of formal documents saying "We are officially working together" or "We are officially not working together", the court has to fall back on attempting to determine the intention. It will have to fall back on looking for any evidence (like that video) that suggests they were in agreement about working together at some point.