Solution to 3D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
5 Coaches retinues (6) TRAINS [DD]
6 Terrible person that might give you salmonella (3,3) BAD EGG [DD]
9 A victory party Hyderabad openers kicked off in Central Court (6) ATRIUM {A}{TRIUMph}
10 Loiter about in posh region’s western suburb, intentionally hidden (8) ULTERIOR {U}{LOITER*}{Re...n}
11 How a wild Arabian may be stopped — like this! (4) WHOA* Semi&lit
12 Vice cell to bust individual? On the contrary (10) COLLECTIVE*
13 Incapable of a light touch? (5-6) HEAVY-HANDED [CD]
18 Studies gripping screenplay’s drafts (10) CONSCRIPTS {CON}{SCRIPTS} (Correction - {CON{SCRIPT}S} - See comments)
24 Freeload off alcoholic (6) SPONGE [DD]
25 Staff accommodating, nearly ingratiating at first, to setter, among others (6) CANINE {CA{Ne...y}{In...g}NE}
DOWN
1 Mixture of oils and spices concocted in a dream (8) MARINADE*
2 Coming off as enigmatic (6) GNOMIC*
3 Find fault with the baroness’s core group of illustrious people (8) ?A?T?E?N (Addendum - PANTHEON {PAN}{THE}{barONess} - See comments)
4 Sorrowful feeling for feathered creature after summer’s end (6) REGRET {EGRET}<=>{s...eR}
5 Crusty as your old cakes and so on (6) TETCHY [CD] (Addendum - {T{ETC}HY} - See comments)
7 Inspect railway going up channel (6) GROOVE G(+r)RO OVE(-r)
8 Abandon a project, turn off life support (4,3,4) PULL THE PLUG [DD]
15 Jumping for joy, extremely energetic tops staying inert (8) ECSTATIC {En...iC}{STATIC}
16 Blood libels regularly resulted in corpses (6) BODIES {BlOoD+lIbElS}
17 You got me to extol the virtues of head cook endlessly (6) TOUCHE {TO}{U}{CHEf} U/Virtues?
19 Salt in track discovered south of water body (3,3) SEA DOG {DOG}<=>{SEA}
20 Walk ostentatiously around tree, for example (6) SASHAY {S{ASH}AY}
Reference List
Posh = U, Left = L, Railway = R