After Lee & Lee*, we developed a family resiliency scale based on the uncovered strengths. If desired, I can supply norms from a general population. If you'd like the actual survey (now, 25 items, 5 subscales). Experience suggests it's versatile and credible for diverse populations.
*Michelle M. Lee PhD & Robert E. Lee PhD (2006) The Voices of Accepting and
Supportive Parents of Gay Sons, Journal of GLBT Family Studies, 2:2, 1-27
I do not know any ready measure of this phenomenon in LGBT parents group. Only Henny Bos has constructed "parental justification scale" and it was published in the article:
Bos, H. M. W., van Balen, F., & van den Boom, D. C. (2007). Child adjustment and parenting in planned lesbian-parent families. American Journal of Orthopsychiatry, 77(1), 38–48. https://doi.org/10.1037/0002-9432.77.1.38
Also in this text you can find some indications:
Bos, H. M. W., van Balen, F., van den Boom, D. C., & Sandfort, T. G. M. (2004). Minority stress, experience of parenthood and child adjustment in lesbian families. Journal of Reproductive and Infant Psychology, 22(4), 291–304. https://doi.org/10.1080/02646830412331298350 The measure depends on the conceptualization of the concept, so the more basic question is: What exactly does "the parental minority stress" mean? It is quite complex idea, it seems to me that it should consider both: the parent himself/herself and his/her worries about the child...
I agree with using a standardized scale. In addition you may want to look at Gregory Herek's LGBTQ stigma work and that of
Gershon, T.D., Tschann, J. & Jemerin, J.M. (1999). Stigmatization, self-esteem and coping among the adolescent children of lesbian mothers. Journal of Adolescent Health, 24, 437-445.
Goldberg, A. E. & Smith, J. Z. (2011). Stigma, Social Context, and Mental Health: Lesbian and Gay Couples Across the Transition to Adoptive Parenthood. Journal of Counseling Psychology, 58(1), 139-150. DOI: 10.1037/a0021684