2D Seal's brood caught (7) S?G?A?S
looks like SIGNALS ?
18A Ask for finger charm (6) A?P?A?
looks like APPEAL
21A Soldier cut out helmet (3) L?D
looks like LID (soldier less LID ... SORE?)
20D Obscure crab (5) ??D?Y
MUDDY perhaps
Just need some help with the wordplays please