A dermatologist prescribes: Resorcine 14g, Salicylic acid 14g, lactic acid 14g and rubbing alcohol AD 100ml

Very much depends on the interpretation of the term disinfectant alcohol. If this is referred to as antiseptic solution (denatured Alcohol 94 °) then no problem can be seen   resorcine dissolves in 0.9 ml of alcohol and salicylic acid in 2.7 ml of alcohol.

is meant ungenerated alcohol 70 ° Then it is very likely that not all salicylic acid dissolves. To suspend the unresolved you can use 1à 2% hydroxypropylcellulose (Klucel)  .  

Since I cannot exclude with certainty all the interaction between salicylic acid and mainly Sulpho resorcinol with HPC, I would personally prefer the first possibility unless the doctor decides otherwise and any form of interaction is omitted..