SQL Server 2017

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CREATE TABLE Customers (
    [CustomerId] int, 
    [CustomerName] varchar(6), 
    [CustomerEmail] varchar(16)
)
;
    
INSERT INTO Customers ([CustomerId], [CustomerName], [CustomerEmail]) VALUES
(1, 'Ben', 'Ben@gmail.com'),
(2, 'Robert', 'Robert@gmail.com'),
(3, 'Paul', 'Paul@gmail.com');

CREATE TABLE CustomerContacts (
    [CustomerContactId] int, 
    [CustomerId] int, 
    [ContactName] varchar(5), 
    [ContactEmail] varchar(13)
);
    
INSERT INTO CustomerContacts ([CustomerContactId], [CustomerId], [ContactName], [ContactEmail]) VALUES
(99, 1, 'Lisa', 'Lisa@msn.com'),
(98, 3, 'Jane', 'Jane@msn.com'),
(97, 3, 'Wendy', 'Wendy@msn.com');

SELECT  C.CustomerId, 
        -- This is needed to prevent FOR JSON PATH to escape the " chars in the Names (and Emails) output
        JSON_QUERY(
            '["' + C.CustomerName + ISNULL('","'+ 
            (
                -- WITHIN GROUP(ORDER BY... is needed to make sure name and emails are in the same order
                SELECT STRING_AGG(CC.ContactName, '","') WITHIN GROUP (ORDER BY CustomerContactId)
                FROM CustomerContacts As CC
                WHERE CC.CustomerId = C.CustomerId
            ), '') + '"]'
        ) As Names,
        JSON_QUERY(
            '["' + C.CustomerEmail + ISNULL('","'+ 
            (
                SELECT STRING_AGG(CC.ContactEmail, '","') WITHIN GROUP (ORDER BY CustomerContactId)
                FROM CustomerContacts As CC
                WHERE CC.CustomerId = C.CustomerId
            ), '') + '"]'
        ) As Emails
FROM Customers AS C
FOR JSON PATH

JSON_F52E2B61-18A1-11d1-B105-00805F49916B
[{"CustomerId":1,"Names":["Ben","Lisa"],"Emails":["Ben@gmail.com","Lisa@msn.com"]},{"CustomerId":2,"Names":["Robert"],"Emails":["Robert@gmail.com"]},{"CustomerId":3,"Names":["Paul","Wendy","Jane"],"Emails":["Paul@gmail.com","Wendy@msn.com","Jane@msn.com"]}]