Eran diez.

There were ten of them.

Éramos cuatro.

There were four of us.

Son dos.

There are two of them.

Somos seis.

There are six of us.

Serán tres.

There will be three of them.

Seremos cinco.

There will be five of us.

¿Cuántos son?

How many of them are there?

¿Cuántos sois?

How many of you are there?

¿Cuántos serán?

How many of them will there be