Littermate syndrome ??

Ha

Hello!

We have a pitbull and boxer puppy who is 4 old. We got him when he was 6 weeks old. We have been in contact with the person we got him from as well as his other siblings. There were 7 pups in his litter. We talk to five of his siblings and keep in contact and update on each others puppies. He is such a good boy and we have been putting him in puppy school and socials and he is doing so well! The person we got him from messaged our group chat and told us that one of his brothers was returned to her in bad condition (never had a shower, flees, scared and timid). She sent pics and videos and he seems really shut down. I can’t stop thinking about the poor pup and my husband and I have been talking about possibly getting him. We have heard about littermate syndrome and are not sure if this would be a good idea. Anyone have suggestions/opinions? We want a second dog but not sure if a sibling would be best? They are both males. Thank you!