im almost done with the mission but i got ambushed by 3 people i cannot seem to beat them any tips?

I looked at Esmerelda and her equipment needs an update. I CoD'ed you some updated items that are level 20, which is the closest i could get. Always update equipment when you can, it will help a whole lot when it comes to your party, and advancing. ^^

Okay, let's see.
At this point, I think you should be able to get your second party slot unlocked by going here and talking to William the Hunter.

Second, as Skyfallthesaberwolf said, your equipment.
There are three major points to Equipment:
Type
Level
Rarity

Type:
What type of equip you should use depends on what Element your pet has (Phys/Str based elements are Air, Earth, and Water, while Magic/Int based are Light, Dark, and Fire), and what you use them for in battle (stat distribution).
The Types of equipment are:
Arcanist- Fully oriented toward Intelligence at cost of all other stats
Ravager- Fully oriented toward Strength at cost of all other stats
(For pure cannon attackers)

Disciple- All-rounder type, adds to all stats equally

Assassin- Primary Agi, Secondary Str
Myrmidon- Primary Dex, Secondary Str

Illusionist- Primary Agi, Secondary Int
Evoker- Primary Dex, Secondary Int

Crusader- Adds evenly to Str and Int
Warden- Adds evenly to Dex and Agi

(Agi tends to be a Tank pet stat, Dex tends to be an Attacker stat)

Level and Rarity:
You typically want to keep your equip level as close to the level of the pet wearing it as possible. However, higher rarity equips have better stats for any given level as a general rule.
Comparison:
Lv50 Epic Assassin Bracelet
HP: 316
Mana: 6
Str: 54
Int: 33
Dex: 33
Agi: 65

Lv60 Epic Assassin Bracelet
HP: 370
Mana: 6
Str: 63
Int: 38
Dex: 38
Agi: 76

Lv50 Legendary Assassin Bracelet
HP: 393
Mana: 8
Str: 67
Int: 41
Dex: 41
Agi: 81

Lv60 Legendary Assassin Bracelet
HP: 460
Mana: 8
Str: 78
Int: 47
Dex: 47
Agi: 94



So currently Esmerelda is a lv22 Dark element (an Int/magic based element) who has three str/phys based equips, which isn't helping her at all.
This is not helped by the levels (5, 10, and 5) or the rarities (uncommon, rare, uncommon)
Persevere!
(If you do need to get equipment for later pets for yourself, you can typically get gold and equipment from mission satchels)