Can my brother be my defacto dependent for express entry migration to Canada?

My parents have been going through rough times for over 5 years now and I have had to look after my baby brother who is 15 years old now. Sometime this year, when my dad fell very ill, he gave me custody/guardianship over my brother. My mum is so occupied looking after my dad that they were all too glad to give me custodianship. I've got the legal documents from the court with both my parents' blessing. I am only 25 years old but have been working and I am capable enough to pay his fees and support him which I've been indirectly doing for the last few years. Now I'm in the express entry pool waiting for an ITA and I'm wondering if it is possible for me to include him in my application as a defacto dependent. It is pointless for me to leave him behind when I'm supposed to fully handle his basic needs & education. Please advise if my adding him to my application will guarantee a refusal of Permanent Residence. If it will, what's the next best option to make sure he's looked after