cats are very adaptable. just give them time to explore it. if they run away, it means they dont like you :-( make sure you have a good relationship with your cat(s) before you take them outside. :-)
its pretty easy acutally. <P>Dont force them into the same room all the time, get them used to each other. Keep them separate and until they are happy with each other don't put them in...
That is hard and you can't make them. Most older cats do not get along with other CATS! But if kittens are introduce with an older cat they have a better chance of getting along.