Child AP and Discounts

[PopGirl26]

in our family of 5, it so happens that DS8 will be visiting WDW more in a year than either adult will. I’d like to purchase a platinum plus AP for just him, because the math works out in our favor.

I just want to be sure:
1. Are we eligible for an AP room discount if the only AP holder in the room is a child? (Should be, right, as his AP is just as expensive as an adult AP?)
2. His MDE is managed by mine. Will photos automatically unlock?
3. Will we be eligible for AP dining and merchandise discounts?

Thanks in advance for your help!