Evelyn for sure. Her elemental defense down makes her a must-max. For the second, I’d max Telluria to upgrade from Yunan myself. Since you’re happy with Yunan, I’d max Zeline. She’s one of the few 5* dispellers that clears everything
Margaret is a joke, even when finally buffed. She is nowhere near Evelyn and Zeline levels. Her only positive aspect is her being very fast and high attack stat but very very squishy I’d rather have costumed Kadilen than her. Morgan Le Fay is good but takes her time killing a target, I would rather have a 1-2 combo that kills in Evelyn and Lianna, eliminating potential threats during raiding or warring. Zeline is there to add insult to injury by debuffing the attacks of the remaining heroes if fired in between the 2 lady rangers.
If this is what you are looking for you still won’t regret Evelyn. Pairing her with your Lianna will be game changing on raids. I’m already enjoying my “poor man’s Evelyn” + Lianna combo. When they are both charged it’s pretty much a guaranteed kill.
I am not too happy having maxed my Morgan. She only gets played as a solo-color support/attacker for my 6th war team. She isn’t bad, but takes no advantage of the general benefits of stacking. For a killer, she is killing very slowly - enough time for enemy to heal up or fire their special.
I have both Evelyn and Zeline maxed and emblemmed. In your case, I would suggest starting with Evelyn (to utilize the devastating Evelyn + Lianna combo at its max potential; but Yunan will also like it), then proceed with Zeline. Zeline’s damage under Evelyn’s debuff is quite significant, also do not underestimate the attack down. If you somehow do not tank with Yunan, Zeline will be great wing/flank for almost any team.