Oh, shut up Amazon. Even ignoring your blatant, entirely unnecessary addition of a sister (if you need to shoehorn in a diversity character, why not just make her his wife, who is mentioned but not named in the books?), just read the bloody source material instead of making up contradictory stuff on your own!

It's technically possible that Isildur was part of Ar-Pharazôn's invasion of Mordor (though no details are ever given of that event), but he would have been the Numenorean equivalent of an early teenager then. And you can't even get battle scenes out of that invasion, because Sauron realized trickery was better than military might in that case and just surrendered right away! The only big army deployment when he was an adult was when Ar-Pharazôn decided to raise an army to invade heaven, which Elendil's family ran away from because they knew it meant disaster. So the entire scene described is just your own fabrication!

And it's not like Isildur doesn't do stuff you could put in the film! I can give you half a season of material that comes (mostly straight) out of the Akallabêth that would work for a TV show before Elindel's family leave Numenor.

First episode, Isildur is introduced as heir-apparent of Andúnië, and is used to show the growing conflict between Ar-Pharazôn (and Sauron) and the Faithful. Second episode, Isildur uncovers Sauron's plan to destroy Nimloth (heck, if you want more girl-power bring in Míriel here as a potential source of the info, as she was likely not on good terms with her 'husband'). Third episode, discussing the situation with his family and heist planning (and here you could have his wife trying to encourage him not to go on a suicide mission, as his "sister" is apparently doing in your made-up timeline). Fourth episode (and maybe a fifth, depending on how crazy you want to make it), the heist itself and Isildur's near-death. Fifth episode, everyone's worried about Isildur (plus maybe angry guards looking for him and his family needs to hide him) but he recovers, and that episode ends with the announcement that Ar-Pharazôn is assembling the invasion force for Valinor.

There you go, half a season of Isildur-focused stuff that actually matches the given material, and then you can do a second half of the season on Isildur and his family preparing to leave. Why do you people need to keep making **** up when you have good source material to begin with?