My addition to Natan 's post:
Usually, a figth between Number of Heroes+1, 2, 3 enemies (depending on the party's capability in combat) and the party is a fight that can end in both ways (heroes can defend multiple times). Of course this is for humanoid or comparable opponents. Concerning this, could you elaborate on the party's composition and on the familiar being played by a player in particular? What kind of creature is the familiar? Did you adjust any stats?
Now, what is probably more difficult is the balance in a figth with beasts, demons, chimeras, undead, faerie, ghosts, ...
Ghosts first, because they are pretty easy: Ghosts are immune to normal damage, take only half of all magical and most sacred damage. Only weapons sacred to a god of death (i.e. Boron, Tairach) do normal damage. Therefore, a single ghost can take out every party without supernatural chars. If there are some, you can go with 1 or 2 ghosts per spellcaster/blessed one.
I would compare hitpoints to determine the number of Undead you can throw against your party. Usually I have 2 zombies, 1.5 skeletons and 1 mummy per char. If there is a blessed one of boron with a sacred raven's beak, I give him at least twice as many enemies, because he can usually destroy one per hit.
Note: I assume that vampires have not been published in English yet, but they are ... crazy.
My faerie usually do not figth. They flee and cast spells. If they do fight, I would consider them to be 1.5 humanoid enemies if they have ~30 HP or as one humanoid if they have <20
Can be considered beasts/humanoids in most regards
are fun. I like to have one lesser demon for every 3 mundane party members, horned demons normally do not need assistence to kill those. For any char that sacred or magical damage I have one lesser demon of a third of a horned one.
Well... size, HP and PRO as well as the number of actions are your indicators for their difficulty. Note that any additional action a creature migth have can only be used to attack. If they are already published in English, use the rules for swarms if you want to have tiny beasts.
Some examples from encounters I had:
- one bear can take out a party of 5 heroes if they do not wear a lot of armor
- a pack of 6 wolves will be a good encounter for 4 heroes of which one wears mail armor
- 40 rats in swarms of 8 were quite easy for five chars
Of course, all these numbers are rather crude approximations as there is nothing like the DnD CR. They are only based on my experience, not on any calculations. And of course TDE offers a ton of other abilities which can be used to manipulate any encounter (combat or not) in creative ways which might end a fight before it even started.