Update!
Today we walked them just fine, they were fine also in the yard, except when Duby jumped on Chase a few times, but most of the time Duby backed off when Chase barked at him. We left them alone in the yard for about an hour, no problems, but it may be because they saw I was in the porch watching them for any behavorial problems =D. They're moving at the end of this week, so hopefully the two will be good before that...