"Who's coming?" might mean
- you're not inviting Bob are you? I'm not coming if Bob is coming
- is this two people joining you for dinner or 50 people all through your house and yard?
- am I going to know anyone else there?
- is this a chance to meet new people?
- I suppose I should sound like I'm interested in this thing and you've already told me when and where it is, so there must be something else I can ask
I recommend you imagine the happier meanings for this question and answer those. For example:
- I'm inviting a TON of people from all different aspects of my life. It's going to be great to introduce you to each other for this celebration. Of course, there will be people you know, like [someone you know they don't have a beef with]. [A category of people they don't know, like "my cousins" or "my coworkers"] will be there too. [You can also list attractions other than attendees, such as activities or food that you have planned.]
This is a warm and positive answer to the question that isn't defensive, doesn't encourage "I'm not coming if Bob is going to be there", and reassures the nervous attendee that they are going to be ok.
If in fact the person needs to know whether you've invited a specific person, they can always ask that. But don't assume that's the reason they're asking.