Congrats on your first fosters! You just have to go about introducing your cat to the fosters the same way you would if you were introducing a new forever cat to the home. Keep them separate for the first night. Introduce them slowly. Some cats accept the new cats readily, others do not. Expect a lot of hissing and growling. Swatting too.

Allen accepts a new foster pretty much right away. Pouncer is a whole 'nother story so I only foster occasionally. Abby does not like female fosters, but ends up getting along after a week or so. Harry loves everyone right away.

Good luck, let us know how the ntroductions go.

PS: that wasn't a long post! Not at all! You shold see some of the novels I write!