Just be sure that your daughters are aware that there is a possibility they will not get to see it, even if you book a VIP tour.
The day we were there in 2019, they were filming or doing something there and we had to bypass it. DD is also a big BTTF fan and was looking forward to seeing it, but we saw enough other stuff that she didn't miss it too much.
Have you thought about the Warner Brothers Studio Tour while you are in the area? It isn't far from Universal and we all absolutely loved that one. Saw a ton of amazing stuff. If your DDs are Harry Potter fans-- and if anyone in the family are Friends or Big Bang fans they will love it. There are also a ton of other movies and shows represented there-- like filming areas from Gilmore Girls, The Music Man and a ton of others. They also have a lot of props, costumes etc on display but I don't know how often they change those out (no doubt the Harry Potter area is permanent I would think)--- we saw a lot from Batman, Aquaman, Wonder Woman, Fantastic Beasts, Crazy Rich Asians and A Star is Born. The tram part of the tour changes depending on where and what they are filming on the lot, but we wound up getting to go through the prop building and also onto the All American (CW network show) soundstage as there were some other areas the tram couldn't go that day. I didn't know All American, but it was still really fun walking around their soundstage--- turn the corner and you completely feel like you are really inside a high school.