You can ask your relative to try Ocean Park next time (though the budget might be double the cost of KFC). I've been there for b'day party twice and their arrangement is quite good. With an english speaking clown.
I have my daughter's birthday party in 2005 for reserve venue 40 people but order the food for 30 people and end up I have 32 peoples show up. At last I paid the food for 30 peoples only.
On that day, there are 3 girls served us and play the games with the kids. We are quite satisfied.
In my opinion, you should not choose either mcdonald or kfc if all guests (or most) are westerner (i mean they don't know cantonese). As these two fast food shop is traditional local store here, and not surprise that they don't have just only one staff can speak or listen english very well. Their requirement of hiring the staff isn't fluent in english but with good service to the customers.... Therefore, i suggest you can have other choices next time.... Maybe Disneyland