With regards to the rental income, no stamping on the tenancy agreement doesn't mean that it can't be taken as income source. Produce evidence of consistent rental collections eg bank statement and the bank will consider about it.

Noted the possibility of the fraudulent act but the banks do consider about it so long as the borrower can show valid evidence and reasonable explanation. The tenancy agreement even though not stamped is still a binding contract, just that it is not admissible to court. On one extreme, stamped tenancy doesn't mean that there are rental receipt as the tenant could have delayed / stop paying or terminated the contract unilaterally.