Why did they use "sea" here?

Question

Hay que tener metas personales claras, apoyos aunque sean solo sin morales, y no tirar la toalla.

Gracias

Answer 1

Aunque sean means "even if they are...." Aunque without the subjunctive means although, so "Aunque son" would mean "although they are."

Answer 2

Good question.

It's the uncertainty, as Pitágoras says, that decides whether "aunque" needs the subjunctive.

1) Voy al cine aunque llueva (I'm going to the theater even if it rains)

Subjunctive because we're not sure if it will rain or not, but in any case I'm going.

2) Voy al cine aunque está lloviendo (I'm going to the theater even though it's raining)

The indicative is used here because it's a fact that it's raining.