Need Help - Letter to US consulate

[chala_pvc]

I got married with my sister daughter. I am inviting my in-laws (brother-in-law & sister who are my spouse parents) to USA. Could you let me know whether I should specify the subject as like below in US consulate letter.

Sub: Issuance visitor's visa to my brother-in-law & sister
OR
Sub: Issuance visitor's visa to my brother-in-law & sister (Spouse parents)
OR
Sub: Issuance visitor's visa to my in-laws(my brother-in-law & sister)

Appreciate your help

[peace999]

).
There can be a denial just on the basis of this unusual relationship,
so I suggest you let your wife do the inviting.
(Inviting her parents)