Merge user lists and ORDER

Is it possible to join 3 tables, two of which contain user names (different users) and then order the list output by alphabetical order?

[code=php]
// table 1
t1.id
t1.event
t1.t2_ID
t1.t3_ID

// table 1
t2.id
t2.t2FirstName
t2.t2LastName

// table 1
t3.id
t3.t3FirstName
t3.t3LastName

// QUERY
SELECT
t1.*,
t2.t2FirstName,
t2.t2LastName,
t3.t3FirstName,
t3.t3LastName
FROM t1
LEFT JOIN t2 ON (t1.t2_ID = t2.id)
LEFT JOIN t3 ON (t1.t3_ID = t3.id)
WHERE t1.event = X
ORDER BY ????? // NEED HELP HERE!
[/code]

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