How can I introduce my friends two castrated male dogs to my 5...all rescues...one male and 4 females...the male loves his girls and is very protective. I would like them to socialise together without disaster befalling any of them!
The basic rule for introducing new dogs is to have them meet at places as neutral as possible such as parks, dog parks, to avoid territorial protection.
Because of the number of dogs involved in your case, I would do it at a dog park.
If it is not possible for some reasons, ie. you don't have dog parks in the area you live, etc., I would let one of your dogs that is the most confident meet your friends dogs first. I personally prefer to do this off-leash (in our backyard, etc.) rather than on a leash (on the street, etc.) so that they can sniff each other more freely.
Then, I will bring in additional dogs one at a time.
Make sure there shouldn't be anything valuable for the dogs at the scene, such as dog bones, rawhides, treats, etc. until you feel comfortable with all of the dogs being friendly.