How can familiars benefit from the Aid spell's temporary Hit Points?

Question

I am about to propose an idea to a friend of mine who plays a Wizard, and whom we have finally convinced should get his familiar up and running. (I play a Cleric in this party). He is concerned that his owl with only 1 HP will too easily die. This is a valid concern based on the experiences we had in our first D&D 5e campaign; my brother's wizard's owl familiar died with some frequency. (This question was inspired by a previous question about familiars.)

I am about to propose that he not worry, since when I cast aid on the party, I can include his familiar. What I am not sure of is whether the familiar (who I think qualifies) to receive the temporary hit points for aid, can be healed if it takes damage less than lethal.

The aid spell says:

Your spell bolsters your allies with toughness and resolve. Choose up to three creatures within range. Each target’s hit point maximum and current hit points increase by 5 for the duration. (Basic Rules, p. 83)

When my cleric casts aid, can my wizard ally's owl familiar get 5 temporary hit points and be healed if it takes damage?

This would improve its chances of survival considerably.

Illustration: I cast aid, owl has 6 HP (1+ 5 Temp). Owl takes 4 HP damage. Can I heal it back up to 6 HP after or during the battle? I am not sure if these bonus HP are like temporary HP, or not.

Answer 1

Aid increases maximum hit points not temporary hit points

Temporary hit points are different as they disappear when they are lost. The aid spell actually changes a creature's hit point maximum. Because of this they are treated as the creature's own hit points and can heal like normal.

Yes it can affect the familiar

Aid affects any creature and familiars are creatures:

the familiar has the statistics of the chosen form

All forms to choose from are creatures.