With Surrounded by Family LTW the first time, I had the first four born to the parents and the fifth one adopted. My founder and gen 2 were both males.
The next time, I had a couple of early children adopted, and then the third one was the heir.
I've also played around with a helper having Surrounded by Family LTW, and my male founder kind of helping with that and having one of the females marked out as his spouse. In the case I'm thinking of it was the Grisbys. Their daughter, Laurel was painter, teen and earmarked as spouse for my male heir. I adopted the next three children, and then the fourth one Ma and Pa Grisby had a boy. That game became glitchy before I could get my founder anywhere near immortality and so forth.
Laurel as teen counted towards this LTW for Ma Grisby (as Mr and Mrs Grisby had already raised her from nooboo hood) and helped out with raising her siblings through the toddler years, having four of them helping with teaching toddler skills was great. Pa Grisby was my sculptor and Ma Grisby was my fisher/gardener (and I think cook). The game glitched in the first generation.
I do have a real cunning plan for my next attempt at the surrounded by family LTW.
I've previously been told in this thread by one of the challenge moderators that under these rules adoption is permitted prior to a natural birth, and that the adoption doesn't affect your next heir ... the heir is simply the first naturally born baby to your current immortal.
Also, don't forget that male immortals don't HAVE to give birth to the next generation until after they become immortal.