The registration deed is fine to some extent, but IMO, most certainly not the declaration from your friend.
To word it more correctly (in IRCC language), the visa office would like to know your *family composition*..... and your *family*, as per IRCC, includes dependents (spouse/common-law partner, children, relatives who are dependent on the host i.e. you).
You seem to be walking the tightrope here. On one hand, you co-own the property with your friend.... but on the other hand, your mom's super visa application is not financially dependent or even dependent for other accommodation/living expenses on your friend.
Can your friend be termed as your 'relative'? How do you guys share expenses? You would know best if your friend can be included as a *relative* i.e. as part of your *family composition*.
Or better still, maybe it would be best to prove your income is way above LICO for three persons (you + your friend + your mom) so that there's no ambiguity or questioning. I would still suggest that you keep it simple