Agree with above comments. Start by seeing if plan language permits non-spouse J&S beneficiary (with spouse's consent if there is one). Most traditional plans do.
A J&S with 50% to the contingent beneficiary will satisfy the restrictions -- i.e., the "incidental benefit" requirements -- regardless of how much younger the non-spouse beneficiary is.
For 100% continuance, non-spouse beneficiary may not be more than N years younger than participant, where N = 10 + number of years, if any, that the participant is younger than age 70 at commencement. So if participant is 65 then non-spouse beneficiary must be at least age 50 -- in other words, no more than 15 (= 10 + 5) years younger.
For continuance %s between 50 and 100 you apply this same rule but replace the 10 by a larger value -- see table in the regs.
Believe that for this rule you measure age at individual's birthday during year of commencement.