Updated 21st September, 2019
4th Wave Now is a site founded by the mother of a daughter who at one point identified as transgender. She has collected a lot of information on transgenderism and has a links page with some resources for children of transitioners (although you have to scroll down a lot!)
https://4thwavenow.com/ Main page
https://4thwavenow.com/resource-index/ Resource Index
Mumsnet’s famous ‘Trans Widows’ thread is currently in three parts. It’s huge, and seems to be the central place at the moment for wives of transitioners to talk.
Sharon Thrace’s TED talk was something I found very helpful. She is a former partner of a transitioner, whose transition came about through his use of ‘tranny porn’. When she says that people don’t want her to tell her story, because it contradicts the popular narrative of transition, it really resonates. Children of transitioners may find this familiar too. Thrace’s partner, Jamie, gave no indication that he might be transgender until his porn use. If your father’s transition is alienating you and other members of your family it might be for this reason.
Colage.org has a page of resources for children of transitioners. https://www.colage.org/resources/people-with-trans-parents/