
I absolutely agree with the others, meeting on neutral ground is essential, then carry on home making out that everything is normal and matter of fact. At home comes the hardest job by appearing to ignore the dogs when actually you are watching body language like a hawk, but they have to accept and allow the new dog on their terms but you have to be fully aware of any change in attitude to nip anything in the bud. Note that they will pick up any tension from you and react so you must really stand back and pretend to leave them alone, but still supervise.
Good luck I am sure you will have a happy doggy family quite quickly, just think of all the extra enjoyment.