So this is initial design from our group..

In this code: x = number of people per invite (doubles as personal ID when combined with invID)
t = text / numbers

guest struct {
int invID // unique field
char surname[x][t] // allows for multiple name entries
char forename[x][t] // see above
char address // one address per invite, so no array needed
char email // similar to above
int attend[x][t] // 0 for no, 1 for yes, 2 for partial (see comments)
char dietary[x][t] // can leave blank for normal, enter text otherwise
char music[x][3][t] // music requests, 3 per person
char comments[x][t] // for anything really, and dietary reqs.
}


/Structure genre of music played--------------------------------------
typedef struct {
char jz; //for jazz
char alt; //alternative
char rnb // for the R&B music
char evrgreen //for old-skool song
}genre_music;//---------------------------------------------------------


/Structure of any circumstances--------------------------------------
typedef struct {
char info; //for the guess who cannot attend early
int person; //person will attend with him
}head_counts;//---------------------------------------------------------

Void circumstances(Gname/ID)-------------------------------------------------
/* Input att_early/att_count*/
/*output ListN/ListC*/
//comments: for the spare food for those who are coming late.
-----------------------------------------------------------------------------

And here we have a function to send out an automated reminder on the day before the party, in email format (pseudocode):

reminder(guest structure)
{
get name and address info for each invite;
mail-merge with premade message or whatnot;
send via email (from the structure);