The Visit guide to the process for making a decision on a visit visa application published by the Home Office says:
“You must also take into account any ongoing financial commitments the applicant has in their country of residence such as rent/ mortgage payments and any dependants who they support financially, including those who are not travelling with them.
Their income or savings, minus their financial commitments, must be sufficient to meet the likely costs they will incur in the UK and be reasonable expenditure in light of their financial situation.”
For the purposes of your application, your dependents are all the people whom you support financially. You must tell the truth and declare all of them in your application. Doing so will not harm your chances of success providing your overall financial circumstances are healthy and your intended spend on your planned visit to the UK is proportionate to your income and savings. The existence of family member dependents in your home country is typically thought of as a tie - something that is likely to compel you to leave the UK at the end of your visit - so could count in your favour.