For red and purple, I would say Proteus and Wilbur should be your priorities. Proteus is one of the best 4* heroes in the game, and with a few mana pots he can pull underpowered teams through the tough final levels of challenges/events. Wilbur is generally an excellent and unique hero and will help massively in all content (especially on titans) and you don’t have other red options anyway.
When you get more warm capes, Boril is a fine choice for your second maxed blue at your stage of the game. using his Riposte skill on raids can help you beat higher level opponents and is great for AoE map bosses too. Although if you manage to pull Grimm at any point, he should become your priority.
For green, it’s between Melendor and Caedmon. In your position, I would go with Caedmon. You have a maxed healer already (Kiril), and a maxed Caedmon would be your biggest single-target hitter by far. Since you don’t really have any snipers (3* Bane and Namahage will only cut it for so long), Caedmon can be your first, and he also dispels which is a requirement in a lot of battles. Another consideration, however, is Tarlak. Since you don’t have Wu Kong, a 3.70 Tarlak would do wonders for your titan scores, which will help you get more unfarmable ascension materials.
In reality though, you need to be building a solid team of 4s, so if you have your training camps at level 13, get them running and try and get a few more of the better TC20 4 heroes (Rigard, Wu Kong, Grimm etc).
You shouldn’t worry too much about your defense at this stage, just try a few things out and see how you go. From what I can see of your current levelled heroes, I’d put your defence as Jack O’Hare - Bane - Kiril - Namahage - Melendor. Caedmon and Proteus go straight in once they get to 3.60.
Hope this helps!
In my honest opinion I would focus on the following for levelling:
Red = Wilbur
Purple = Proteus
green = Melendor and Tarlak
Blue = Boril
That’s one good looking pull!
I think you need a few more 4*s leveled up, looks like green is a strong color for you, and yellow is weak.
Proteus and Wilbur are great heroes that should get prioritized over any of the others in their color. Up there with Kiril as some of the best 4* in the game.
Tarlak is an amazing titan basher, you may want to consider bringing him to level 2.60 maximum. That will give him semi-sturdy stats and his skill will probably max by then. I recommend that so you can focus first on maxing the 4*s since they take less time to max than 5*s; for your point in the game it’s better to have several good heroes, rather than a few great ones.