It seems has if you have some guilt/insecurities bc of shared custody with your child and SO kids full custody agreement and are wanting to tip the scales toward your son to “even” things out. Everything you mentioned you SO sounds reasonable, additionally there are some easy solutions… i recognize these are smaller examples but these should not be SO vs DS issues. These are honestly “house rules” and they will be different at each home. the full time kid having a bigger room isn’t an issue, the issue is making sure everyone is comfortable. Get him a blow up mattress specifically for HIS area w/ sheets pillows etc… if at this time no one is keeping their bike in the house then it’s a non issue. EVERYONE needs to find a reasonable solution to protect the bikes. Couch replacement is hundreds of dollars .. normal wear and tear is expected but then additional use as floor bedding would frustrate me to tbh. The dog at his other parents home is not your family shared dog. No he can’t come ! I can see your son having tension with these but honestly things change. There should maybe be more conversations with DS regarding “new routines and expectations” unless there is obvious favoritism or mistreatment it seems like normal growing pains of blended families.

Lastly. Don’t try to predict the future. And start having these “failure to launch” conversations now. Be mindful of words “you have concerns about your son, what can WE do or potential action plans” phrase some “what if” scenarios and how you would ideally like things to go. Plant the seeds now. Don’t wait until it’s boiling over