Hi Anindya,
I'm afraid you are approaching the reporting task in the most complicated and probably most inefficient way.
First of all, it makes sense to check which standard (out-of-the-box) reports from transactional system could be used - there are quite many of them, relevant to Treasury, dedicated to various aspects in the whole process, like FTR_ALERT, FTR_00, TJ04, TPM12, TPM13, TPM40, TPM20, etc. The big advantage of these standard reports is that user is able to modify them on his/ her own without the need of programming.
Next, if there are some cases - that's quite common also - where standard reports are not sufficient, then you could use so called Logical databases, such as FTI_TR_DEALS, FTI_TR_POSITIONS, FTI_TR_PERIODS, etc. In combination with the SAP queries, they are simple and powerful tools for creating reports that particularly meet your specific requirements.
Finally, you can create reports, by ABAP or SQL server as in your case, though this is rather time consuming process, also requiring very specific knowledge about the content of these tables.
And I'm afraid there is no one and simple answer to your question: 'Can anybody help us out in understanding the Key relationships or joining conditions in SAP Treasury Module' as again it depends on the context what functionality is going to be implemented at Customer.
Kind regards,
Renatas