combining 2 strings in objective-c-Collection of common programming errors

I have a problem when I try to combine 2 NSString

I extract 2 NSSring form a JSON and its diagrams are:

thumbList: ( “picture1.jpg”, “picture2.jpg”, “picture3.jpg” … )

fullnameList: (“name1”, “name2” , “name3” … )

My intention is unite them into one using the following scheme: (“name1”, “picture1.jpg”, “name2”, “picture2.jpg”, “name3”, “picture3.jpg”…)

NSArray *array_webdata=[[NSArray array] init];

NSString *searchStatus = [[NSString alloc] initWithData:webData encoding:NSUTF8StringEncoding];    
array_webdata = [parsedata objectWithString:searchStatus error:nil];

//String with all data of each user
NSString *usersList = [array_webdata valueForKey:@"results"];    
NSLog(@"\n results? = %@ \n", usersList);

//String with thumbs
NSString *thumbList = [usersList valueForKey:@"thumb"];
NSLog(@"\n thumbs? = %@ \n", thumbList);

//String with usernames
NSString *fullnameList = [usersList valueForKey:@"fullname"];
NSLog(@"\n fullnames? = %@ \n", fullnameList);


NSMutableIndexSet *indexes = [NSMutableIndexSet indexSetWithIndex:1];
[indexes addIndex:3];    
[fullnameList insertObjects:thumbList atIndexes:indexes];
NSLog(@"array: %@", fullnameList);

But when I try to execute shows the next error message: [__NSArrayI insertObjects:atIndexes:]: unrecognized selector sent to instance.

Can anyone help me?