It seems like we're doing better on both issues...
I cut back a little on the new food to allow him to get used to it and as for potty I restrict him so he has no choice but going to his pads. I didn't think about the option that the other Yorkie was marking, he is too young but you actually might be right... ohh well, we live and we learn...
Next time we'll go to the dog park
Thank you so much for you input!!