Field Marshal

Other Soldier creatures get +1/+1 and have first strike. (They deal combat damage before creatures without first strike.)

Captain of the Watch

Vigilance (Attacking doesn't cause this creature to tap.)
Other Soldier creatures you control get +1/+1 and have vigilance.
When Captain of the Watch enters, create three 1/1 white Soldier creature tokens.

Daru Warchief

Soldier spells you cast cost {1} less to cast.
Soldier creatures you control get +1/+2.

Valiant Veteran

Other Soldiers you control get +1/+1.
{3}{W}{W}, Exile Valiant Veteran from your graveyard: Put a +1/+1 counter on each Soldier you control.