I agree, he is likely still bewildered and adjusting. Thank you for adopting this pup!

His body needs to adjust to whatever food you are feeding; likely not what he had at the rescue or in the shelter (which ever), and certainly not what he ate at the hoarder's. Once that happens, and with a consistent routine of walks and feeding times, you can figure out his schedule. I have 2 dogs who pee immediately after eating, and 3 who pee an hour after. (I need a revolving door!) Anyway, that will help. Then you adjust his walks to that time frame. Same for BMs.

Does he sniff around at all when outdoors? I have one girl who will sniff and when she finds the "right spot," she spins in a circle before pooping. THAT helps alot, but only one of mine seems to have such an obvious clue.

Having other trained dogs around will help him plenty. For now, patience and routine and patience.

Does your 2 year old try to engage him in play? She must, if she is quite playful. Can you describe his response?