Use Custom module as Products Module.

Use Custom module as Products Module.

hi

We are using the Zoho CRM for Real Estate company. We sell property (products) to contacts.
I tried to use the Products module to store all the property detail. but the problem we faced is that we can not have Many-to-Many relation between Contact & Products because one property (Products) can be bought as joint owner (2 contact) or one Contact can have many property (Products).

The solutions to my problem (M-to-M relation) is to use Custom Module instead of "Products" module. but i dont know how to use the record from this custom module in Deal and Quotes as line Item. Please note that I need to send quotes using Zoho Sign from "Quotes" Module. 

Does any one has any solution/idea on how to use the record from Custom module as products?

Thanks