Any FE Genealogy player here?

Yes, because the shoulder pads are the only things they increased in size. :l

As far as I can remember, none of the Gen 2 units die. Could be wrong, it's been a while. But I'm sure Lene and Ares survive

The Second Generation cast of FE4 survives by the end of the story, the first generation don't. However, permadeath is a thing in FE4 so if your Lene dies in the game she's considered dead but canonically, no.

Ishtar's fashion decisions are difficult to understand but her appearance is very 90's.

Yeah as far as I recollect (played it a while ago on the bad translation patch) they live. They all do if you play your cards right as per usual.

And not only did Ishtar's shoulder pads get bigger, her entire body got an upgrade. I prefer the og, but Ill leave a pic of her here for you to see the changes. And warning, the image may look different cause of reasons. Seems to be happening recently so just putting it out there

My favourite fire emblem <3
Nobody dies in second generation (except the deaths cuz the player). But in first generation her mother dies in Barhara's Barbecue. It's curious that feh made canon the relationship between Claude and Sylvia for the Bragi's blood.

P.D. Reinhard approves Ishtar's new oppais XD

FE4 is my favorite game in the series!
As for your question on Leen, well, she either lives, dies, or doesn't exist at all.
She lives if you pair Sylvia up and keep Leen alive throughout the second generation. Canonically Leen doesn't die, but if you slip up and get her killed, she technically is dead. It's possible for Leen not to exist if you don't pair Sylvia up; In that case, her substitute version, Laylea, joins the party instead.

Lene can survive by the end of the game unless she ends up getting killed by an enemy. Which isn't too hard at all, because It's a bitch and a half to train her up because of her low attack though she isn't built for combat anyway.

If she does die however, it's possible for her to be revived with the Valkyrie Staff if Claud is the father of Coirpre (and Lene herself, for that matter) or Ced.