Dog socializing tips please?

I house sit/dog sit for a guy who has 2 high strung Maltese (about 4 years old). When walking them, they yap and yap at any other dog walkers in the area and they have proven to be quite territorial. For the first time, I need to bring my 1 1/2 year old black lab over while house sitting for him. My lab is very social and gets along great with other dogs, so I don't really see any problem on her end of things. However, I have seen that when the Maltese are under alot of "stress", they won't eat or sleep right. Any suggestions to help them get along? We have set up a "socialization" meeting for this weekend before I watch them over a week span.