Pawla,

Never say never. Cats CAN be introduced gradually if done properly.

Try putting the newbie in a room with his catbox, food and water. Play classical music on a radio and go in and visit every chance you get. Rub him down with a towel an allow the older cats to smell his scent, then vice versa. Stack a couple of baby gates in the doorway and let the cats see, sniff, growl, hiss, whatever. After about 2 weeks, take down the gates and let them be. Have a spray bottle handy just in case. There WILL be growling, hissing, spitting. As long as there is no bloodshed, just let her show him where he stands in the hierchy.

Male/female is alot easier, believe me. Of course, that's only my opinion.

I would give it my all if I were you. He needs someone like you.