I find this to be a very interesting video - the whole 8 minutes of it.
What I see is Sid back on one of her favourite perches, the one that Ellie uses quite frequently. We see Vic leave his usual perch and come into the nest to get in more practice. Watch how attentive Sid is as we watch Vic make several take offs and landings. It’s almost like Sid is encouraging him. Eventually Vic not only takes off but ( for the first time I’ve seen ) lands on a new branch for him!
I do try to avoid anthropomorphism but it so hard not to at times. Having said that I wish I knew if Sid is somehow encouraging Vic ? In my head I imagine Sid saying “you’ve got this-there you go - you can do this!”
After a couple of more attempts Vic heads back to his usual branch.
Later in the day my wife comes in to announce that both eaglets were flying between the trees next to our house!