When you're telling your extended family, let your relatives know that
- you're the one they should come to with questions, not your child;
- you expect them to support your child; and
- you're willing (or happy, if you can say that honestly) to address any concerns they might have.
If your child receives a negative reaction from a relative, support them and advocate for or with them.
If you're not telling everyone, make sure those you share this information with know who is and isn't in the loop. Emphasize that the decision to come out to others is yours and your child's alone.
Make sure to set boundaries, in consultation with your young person, about what details you will and won't share with your relatives. Does Uncle Joe get to know if your child is on puberty blockers? Can Grandma ask about the safer sex information you may have shared with your young person?
Be clear, within yourself and with your relatives, about any limits to the support you provide them. If Aunt Sue has already tried to dissuade you from "humoring" your child, you do not need to have that conversation again. Ditto if Grandpa asks the same question over and over, not because of dementia but because he's hoping he can badger you into a different response.
If one of your in-laws comments about how this is "your fault" for giving in to a child's "whims," please discuss this as soon as possible with your partner/spouse. Do not let your extended family drive a wedge between you. Having a child come out can be challenging enough for parents; family does not need to make it harder.
Be aware of the "winter holidays" in the US -- Thanksgiving through to New Year's. If you're outside the US, you likely have similar periods of festivals and holidays that run back-to-back and/or that go on for multiple days. Or you might be in the Southern Hemisphere where December and January holidays are in the summer.
Regardless of where you might be located, these times are often filled with many family gatherings, which can be very challenging for young people who don't have supportive relatives. Ditto for the supportive parents and siblings of queer and trans tweens and teens, who may also have a rough time.
Strategize with your child in advance of the holidays about what gatherings they need to attend and which ones they can skip. For those they can't get out of and that are hosted by unsupportive relatives, is there a space in their house that your young person can escape for a few minutes, like a bathroom or bedroom in a less trafficked part of the house? If you will be hosting, can your queer or trans child spend that time somewhere else, like at the library or a friend's house?
Discuss in advance what your child's boundaries are. Whom can they tolerate bias or misgendering from? Whom can they ask to intervene for them? How much screen time is healthy for them? (If this is a road you tread over repeatedly and your child wants more screen time than you're comfortable with, you may not want to bring this up here for yet another argument.)
And if your young person wants to use winter holiday gatherings to come out to everyone, talk with them about that likely not being the best decision. These events can already be so fraught. Introducing queerness and/or transness into them can make them harder for everyone. Your queer or trans child may be more successful in getting a supportive -- or, at least, neutral -- reaction to coming out if it's not on a major holiday.
(My gratitude to Page of the Common Goodness Project for the thoughts about holidays above.)
Your absolute top priority is supporting your child and building for them the most affirming family-community possible. A very close second is taking care of yourself and your own emotions during this process.
Keep in mind that there are other sections of Reflecting Rainbow Tweens & Teens for different family members. If any of those resources seem like they might be helpful, please consider passing them on to your relatives.