what is the best way to introduce my sons cats to my lot?

hi my son is having to move back to my house with us he has 2 indoor cats, big tabbys boys toby and tyler they are twins, i have 7 indoor/outdoor cats, 5 boys 2 girls, it is a very safe area where i live lots of fields no busy roads no preditors etc, he is moving in 2 weeks i have taken the week of work to settle the cats in, they are not used to other cats my lot are quite tolerant of other cats, most of my neighbours have cats, does anyone have any suggestions to make the transition a little easier for toby and tyler, they have a very close bond with each other, i dont want them to be frightened here new home new cats etc any help would be usefull thanks