Stop leveling and ascending everything.

Take your elhain to 6 stars/ascended/booked/masteries. This will be your campaign farmer for a long time, used to farm 12-3 brutal. 

Yeah. Priority 1 is getting a campaign farmer to 60. You may not need to give Elhain masteries to do that, I honestly can't remember since it's been so long.

Then, in terms of who else to take to 60, Khatun, Magnarr, and Rathalos are good choices. You need a support champ with revive/heal/speedup to round that team out; you'll eventually get Scyl for that spot, if nobody else.

With your Roster, taking Elhain to 60 as your campaign farmer is the easiest choice.  However, if you do not want to do that (for whatever reason), you could get away with farming campaign with Rathalos.

As for the Forge Pass, I wouldn't buy it at your level of game progression.  As for the pieces you forge just from completing it, that is damage gear that is not focused on either Atk or Def, so you can use that gear on any damage dealer to good effect.    

Thank you @evilized6666 , @kramaswamy.kr and @WileyMan ! I will make Rathalos my lead and try to take Elhain to 60. 121 days until Scyl...

I will also try to summon some more champions

Except like ... don't. That's probably THE number one mistake newer players make ... possibly alongside using epic/lego books wastefully. Don't summon more champs. Like, if you ever open the game and see that shiny portal enticing you to press the summon button, just tell yourself "kramaswamy said don't do it, so I won't".

Literally do not use those shards EVER, unless you are doing so as part of a fusion event.