Refinancing-Disclosure of other loans

Yes you should disclose ALL other assets, liabilities /  commitments as this may have an impact on your serviceability (ability to repay etc). Most Loan Applications will include a declaration that all information provided is true and correct (read the fine print).

Lenders will at least get a CRAA (Credit Check report) which will show previous credit enquiries along with any defaults & judgements etc. Depending on the lender and how thorough they are may query any previous credit enquiries and even for some too many enquiries may involk an automatic decline.
Some lenders may also conduct Titles Searches (by borrowers name) to identify / confirm any other properties owned, these titles searches will also show registered mortgages on these properties.
Often discovery of non-disclosure of other liabilities or relative information will also involk an automatic decline however in the interest of 'making a sale' this may be overridden.

I believe it is always best practice to give full disclosure of your situation to enable the prospective lender to be fully aware of your situation

In addition to the post from MarJac your credit file will also show a list of companies you are director of. Often banks also complete ASIC searches that show if the company is trading and if the company has any charges e.g. Loans for cars etc.

Non disclosure of debt is very common however the new legislation (NCCP) will put more accountability on managers and brokers that do not disclose debt (noting if debt is disclosed the deal might not service – therefore be deemed unsuitable for the client).

If you ever end up in a collections and the bank discovers the deal was fraudulent you could be in strife as the courts will give the banks almost free access to all your assets to recover debt.

You also face potential fines and jail if convicted of fraud – very unlikley but possible if the bank lost money based on a false declaration.

It is the same as not disclosing how many dependents you have – no easy to justify how you forgot about your kids… Also noneasy to forget you own another property.