For screening, you can follow the ultimate BP screening guide. don't skip steps:
https://www.biggerpockets.com/...
My process for accepting applications is as follows: the first person to submit a fully completed application, meets my criteria AND turns in the holding deposit (which becomes the security deposit after lease signing along with receiving first months rent), I will take the property off market and stop marketing the property. Until then, I continue accepting and processing applications. You could have an applicant who you accept, but has instead found another property by the time you accept. tenants are shopping around, so you dont stop until they back up their interest with a security deposit or sign the lease (and provide deposit plus first month rent).
You cant discriminate against family members. You can only evaluate the adults againsts your screening criteria. Look at their ability to pay, proof of income, check their landlord references by calling them, then look at their credit report to confirm their ability to pay their rent against their current liabilities. Does their income leave enough to pay the rent after all of their bills on credit report? Then accept the best one, but dont reject the other applications until the top one submits their holding deposit within 24 hours. If they dont, you have other applicants you can accept without having to start the entire process over again. This is why you want many applications and be able to pick the best option. Good luck!