Solution to 13D 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.
Open for anyone to solve, if not solved by 1 PM.
ACROSS
1 Isolation of person and family trapped in liberal societies (10) LONELINESS {L}{ONE}{LINES}{S}
6 One's inclined to bring people up (4) RAMP [CD]
9 Downloads a bad smelly specimen (10) SANDALWOOD*
10 Open, switch hands, and run (4) FLEE F(-r+l)REE
12 Suspect witness aims to get sweetheart arrested - they need to be separated right away! (7,5) SIAMESE TWINS {WITNESS+AIMS}* over {swEet}
15 Husband and girl (French one) with a weapon (7) HANDGUN {H}{AND}{G}{UN}
16 Time wasted in depression almost always more difficult (7) ROUGHER {tROUGH}{'ER}
17
Dance record followed by one hundred thousand (7)
ROLLICK {ROLL}{1}{C}{K}
19 Novice gridmaker cycles those in white squares (7) LETTERS {L}{(-s)ETTER(+s)S}
20 Slower than the best... it's secret? (3,3,6) OFF THE RECORD [DD]
23 Unacceptable to return, after hemming, posh coat (4) DAUB {B{U}AD<=}
24 Turn child on bed - else turning can result in haemorrhages (10) NOSEBLEEDS {SON<=}{BED+ELSE}*
25 Residual force yanks top off (4) REST wREST
26 Belatedly sad - after son's time of expiry (4-2,4) SELL-BY DATE {BELATEDLY}*<=>{S}
DOWN
1 Green and red, not blue (4) LUSH bLUSH
2 Time of day devoid of love and energy - not a bit (4) NONE {NOoN}{E}
3 Famous person - angel - hid guilt somehow, not for all to see (7,5) LEADING LIGHT {ANGEL+HID+GuILT}*
4 Southern people follow contemporary TV personalities (7) NEWSMEN {S}{MEN}<=>{NEW}
5 Finance partners joining trail (7) SPONSOR {NS} in {SPOOR}
7 Politician finally boards a large boat for an extended period of work (3-7) ALL-NIGHTER {A}{L}{L{p...aN}IGHTER}
8 Force media Union to resist (10) PRESSURISE {PRESS}{U}{RISE}
11 Beginning to crumble, when surrounded by support, you finally fight back systematically (12) STRUCTURALLY {STRU{Cr...e}T}{yoU}{RALLY}
13 Fast food owner's on vacation - daughter's quicker to cover (5-5) ?H?R?-O?D?R (Addendum - SHORT-ORDER {SHORT{OwneR}{D}ER - See comments}
14 Crawling, falls on our ground (2,3,5) ON ALL FOURS*
18 Amateur artist with nothing, captured by kings, gets threats essentially, provides entertainment (7) KARAOKE {K}{A}{RA}{O}{K}{thrEats}
19 Milky yoghurt initially spurned by prowling alleycat (7) LACTEAL ALLEyCAT*
21 Fluid from ears, oozing (4) SERA*
22 One surrounded by water often dissolves (4) ISLE dIsSoLvEs
Reference List
Liberal = L, Societies = S, Husband = H, Girl = G, One in French = UN, Time = T, Hundred = C, Thousand = K, Novice = L, Posh = U, Son = S, Blue = B, Energy = E, For all to see = U, Amateur = A, Artist = RA, King = K