I found this a little harder than usual, solving time 27 mins.
* = anagram
ACROSS
5 P(L)EASANT
9 HAM PER
10 MARK ET
11 A NOR (E XI)A
12 HURSTPIERPOINT (support in their)* I’d to go to Wikipedia for this.
15 STRESS (sisters)* less i
16 ELDERS Double definition
18 RUNNING BATTLES
20 CA (SHED) IN Cain and Abel
22 I NDUCE n moving in dunce
24 SLAL (O) M o in (small)*
25 SINECURE (Nice ruse)*
DOWN
1 BANK I think, my last entry, double definition (save in a bank, and bank of a river, I think)
2 S(HO)O
3 IMP E NITENT (intent)*
4 HE RIOT Old word for fine on death that I confirmed after
6 LEAGUES (See Gaul)*
7 AN TIP ASTI
8 TRACE Double definition
13 STRONG HOLD
14 PALLADIAN (a plan laid)*
17 Sir Stanley SPENCE R Sir Basil Spence, architect r = rex
18 RE ALLY My favourite clue “About to bond with friend, without a doubt”
19 GEN US
21 DAME haD A MEal losing ‘bits on the side’
23 DOCK Double definition