I'm looking at some of the low hanging fruit so to speak for issues reported as of 1.5.

Familiar can't summon Air Elemental or Crag Spawn

I looked at the CoreSpells.xml and noticed that <Range>0</Range> is missing from these two summons.

After adding that line both of these spells are now able to be summoned by the familiar. There may be other summons affected as well. I only tested the summons I could enable using the cheat commands with Ceresa. 

Level 1 Familiar Bug

I replaced 

<GameModifier>
<ModType>Unit</ModType>
<Attribute>SummonUnit</Attribute>
<UnitClass>Familiar</UnitClass>
<Duration>-1</Duration>
<Value>1</Value>
</GameModifier>

with

<GameModifier>
<ModType>Unit</ModType>
<Attribute>SummonUnit</Attribute>
<UnitClass>Familiar</UnitClass>
<Duration>-1</Duration>
<Calculate InternalName="Calc">
<Expression><![CDATA[[UnitStat_BonusSummonLevel] + 1]]></Expression>
</Calculate>
<Calculate InternalName="Value">
<Expression><![CDATA[[Calc]]]></Expression>
</Calculate>
</GameModifier>

Familiars start with the bonus levels from the caster. If anyone would like to try these fixes I unzip the file in the external link and drop them into the mod folder. Make sure to enable mods and you will need to start a new game.