Over the years, researchers have developed various theoretical models regarding sexual orientation and gender identity development, including:
Models of sexual orientation (LGB) identity development
One of the first models of sexual orientation identity development was developed by Vivian Cass (1979). It is a six-stage model that describes the developmental process that individuals go through as they consider and then acquire their identity as a lesbian, gay or bisexual person.
The main issue with Cass’s model is its description of the stages as fixed, but today we understand sexual identity development as a more dynamic and fluid process. Therefore the other model to introduce to your participants can be Dillon’s more recent (2011) multidimensional model, which includes individual and social aspects as well. He describes 5 phases that are non-linear and flexible:

Dillon, Worthington, Moradi, B. (2011). Sexual identity as a universal process. Link to paper here.
Models of gender identity (T) development
Coming to recognize oneself as gender-variant or transgender person involves stages of exploration and analysis on both interpersonal and intrapersonal levels over the course of many years. Considering usually multiple minority statuses of transgender people, their special challenges due to the transition process, Aaron Devor (2008) describes his model of transgender identity development that encompasses 14 possible identity stages until complete surgical gender reassignment. It is important to emphasize constantly that not all transgender people want or have access to the entire transition process due to various reasons: their residence, financial reasons, medical conditions etc. The stages in this model describe a process that is a little bit similar to what we see in Cass’s sexual orintation identity development model:
Amongst many differences an important one is the possibility of a gender affirmation/transition process, which in itself is a journey: the acceptance and integration of the post-transition gender identity can be a long process too.
Pinto and Moleiro’s model of transgender identity (2015) does not pathologize trans identities, defining five stages of transitioning, regardless of age related experiences.
In general, one′s experience of mind-body dissonance is the starting element: this realisation comes early in childhood that their experiences and impression of their gender do not match with their physical bodies. Puberty can be an upsetting experience, where the bodily changes can lead to negative feelings towards one’s body, especially when it comes to the changes of the female body with the development of secondary sex characteristics and the onset of menstruation. The feeling of dissonance moreover can be visible in feelings towards dressing expectations (dressing is an explicit way of gender expression), and also regarding activities. In the absence of support the feelings of dissonance are repressed or at least hidden, even until early adulthood. Starting the process of transition – which can mean any form of transition that is found suitable by the individual – is considered the breaking point by this model, when the individuals start to accept and live by their gender identity.