Seeing some of the responses thus far with discussions about the type of teams being used in Hard Mode, it is not difficult to see that those players with leveled 5* heroes will have a comparatively easier time on these than those that don’t.
I don’t have too many serviceable 5* myself. I have been doing the Hard Stages kind of progressively as each provinces are released.
My main team that I have been using are Boldtusk, Melendor, Cyprian, Gormek, and Wu Kong. All maxed 4* and this is what I had to work with, even before Emblems are introduced. I’ve progressed through approximately 15 provinces with that lineup, starting from 16 and up is at or around when emblems were first introduced. I eventually swapped out Gormek with Isarnia, who finally become serviceable at / around 3rd / 4th ascension and the others kept relatively the same (but added emblem points to further augment their stats).
Hard Mode is doable with 4s, but you just have to watch them more closely, 3 is generally a bit on the weak side, and might still be serviceable on normal mode, but on hard mode maxed 3* may actually die in the first hit or two. On hard mode, not only are enemies hitting harder, you are also doing less damage, so you can see from the lineup that I use, I try to have multiple healers, buff attack, debuff and dispel enemies, and increase my tile damage. Having Gormek will help against green enemies for the tile damage, but before Isarnia was swapped in, I was not really doing much against red enemies. Plus, aside from the slow mana charge, there is no blind spot to hide from her specials (unless blinded, affected by Wu Kong’s Gambler’s Stance, or on Dense Fog stages).
Melendor is obviously a bit of a squishy defender, but he still has high offense and can help against blue enemies (can’t get that with Sabina), so it is not hard to see I have had to baby him the most, but having the ability to dispel enemy buffs or counterattacks without having to hit them first is a plus.
But for ailments, unless there is a Rigard in your party (but you still got to time him just right), Antidotes (the small ones), is your best friend.
Wu Kong is there to buff up my tile damage and is useful to up that on top of Boldtusk’s attack up.
Cyprian is there for his counter attack, and I usually have him flanked by low defense team mates so the harder they get hit while Riposte is on, the more damage the enemies take. I’ve had a few boss enemies doing AOE damage and ends up killing themselves. I am not a great strategist when setting up cascading tiles, so Cyprian was a very important catalyst in me passing some of these Hard Mode stages.
Items are going to be quite standard in what you bring. Going through a few stages, there are some in which I feel more comfortable to bring Dragon Attack/Bombs, and the rest are mana / healing potions, but I would sub out one of them (perhaps mana, for the antidote if I foresee the bosses potentially doing heavy wreckage with their ailment inducing specials).
You have some very similar heroes as who I am using (BT and Melendor), but I would like to comment that Hard Mode is doable and manageable if you are careful and bringing items.
Try a few stages to get a feel for how hard the enemies hit. Don’t be surprised if you find that the first mob is often the most difficult because none of your heroes are “mana-ed” up and you are going through the gauntlet of having to get them to survive the first wave of hits while your heroes charge up their mana. Good luck.