There is zero difference in dynamics in a gay family unit from those of a straight family unit. I have seen many adoption situations and my other half and I ended up with our Nephew when the "dynamics" of his "straight" family became so unhealthy that the kid nearly had a complete breakdown.
The question you ask to me is the equivalent of "Who plays the boy and who plays the girl?" which my friend is demeaning and insulting. We got this question from a "Niece" when she was about 14 years old.
I cannot speak for all gay families. What I can tell you about ours is that there is incredible communication. Our Nephew is well aware he is totally unable to play one of us off the other, and he is aware that his Uncle Shawn barks, but it is his Uncle Ken that he needs to watch out for because he is the one that bites and bites hard. Of our family I am the more dominant personality and in that single sense, if there were to be a male gender role, then I would probably be it. I am 5'9" and 190 pounds of "Bear" and my other half is 6'5" and 207. Neither one of us are in any manner effeminate. We live on a horse ranch north of Deming, NM and hobbies include hunting, fishing, automobile and boat racing and collecting vehicles.
On some other family unit the dynamics might be different. The love and support and teaching the child to be goal oriented are important, the idea of making that child the best and most productive person he or she can be are the issues. It does not take two people of the opposite gender to accomplish that task.
When we lived near Palm Springs, California and before the responsibility of our Nephew came into our lives one of the bar tenders at a gay bar we knew one evening relayed a story to me.
He tended bar at two different men's bars in the evenings and he tended at a lesbian bar during the early afternoon shift.
On a slow night he relayed the following story: He was present when there was a conversation between two very masculine leathermen. The conversation was the amount of profit that they had jointly made from hosting a "Tupperware" party. That same morning he had enjoyed a conversation with two lesbians who were discussing the intricacies of rebuilding the flathead V8 in the 1949 Ford they were restoring.
To not understand dynamics or or consider them different this would tend to indicate that you asking the question maybe consider some stereotypes to be accurate. Dynamics are two parents trying to do a job and because kids do not come with an "owners and operators manual" they do the best they can with what they have to work with just like any heterosexual couple trying to undertake the same task