Among your choices, I only have Malicna and Grimble both at 3/70. My other 3/70 purples are 2nd Clarissa, Zulag, Kunchen, and Quintus, while I am still working on Obakan to get to that level, currently at 3/60ish. I have other unleveled purple legendaries like 2nd Kunchen, unleveled Domitia with costume (2nd copy, in reserve), another Zulag, and an unleveled Sartana (2nd copy). After I get Obakan to 3/70, I plan ascending Malicna first as I like the possibility of her higher defense debuff and that I can emblem her maybe up to +10. After her, I intend to max Grimble, who may be lightly emblemed as he has sturdy stats and his main function is only to kill minions, which does not really pose much of a problem for me even without a minion buster I would like to use. Currently, I have 26 tabards.
My maxed purple legendaries are Alfrike, Panther, Kageburado, Seshat, Clarissa, Domitia and her costume, and Sartana. I use mono and I split them into 2 teams, supported oftentimes by my other epic purples like several Rigards with costume, Ametrine, Sabina, and Tiburtus with costume. I do have other maxed purple epics but they are mainly relegated to events and raid tourneys. I have 5 purple mana troops to at least level 11.
However, there is really no rule requiring you to max more legendary heroes unless they are the prized ones ideal for offense, defense, titans and events. In your selection and in your roster of heroes, I’d suggest you wait for better ones and work on some dupe 4* purples instead, especially those that are very helpful in your attacking preferences in wars for depth.
Just my 2 cents.