i feel so sorry for you & your baby. seriously it sound like a very complicated relationship you have. first it's dealing with your in-laws, then your parents & then a husband who doesn't want to take ownership in handling baby matter! you r very stuck & i know it worry you about your baby then the adults. i think it'll help a bit if your hubby can tell his mum want he would like to see & what is his comfy zone, of cos cannot mention it's being discuss with you. . parents work better with their children. so you can negotiate with your mum better.
i do occasionally feed my 5mth baby on Jin Feng powder, you know, the stuff old ppl say to give if baby seem to had a fright & cry non-stop. i dont feed that often. everyone has different way to bring up their children. my hubby likes to remind me, he said something along that line "Your parents bring you up & you look fine to me, dont't worry too much" I cant recall the exact words but it works on me. i'll tell myself not to panic when it comes to my parent taking care or when my-laws are taking care. my hubby grew up to be a fine man! well, i hope that statement makes you feel a bit more at ease when you feel helpless about your situation. in your case, your in-law didnt look after your hubby at all? how about sibling? although it doesnt reflect they cant look after baby.....
i have been feeding my 5mth baby on the stage 1 nestle too but it's plain rice cereal. it's also stated only for 6mth onward. of cos i notice there r baby food for 4mth +, never try it.
how's your baby length & wt? is it a concern? over weight? underweight? looks fine & good? happy baby? of cos taking away the fact she has cough & may not seem lively. if her growth is well, then maybe not worry too much? if you can control the situation then of cos that is the best but offending lots of care giver now, is not a wise option.
if their upbringing is harming her well being & you r feeling very strong against it, you take over & quit. of cos you need to discuss with your hubby & tell him you r feeling the stress over conflicts in taking care of baby. you needed him to help you tide over difficult time like this.
Or take the chance to see a paediatric & tell doc your concerns over ling yang, wheat honey & charcoal. see what the doc comes up with & make sure your hubby is with you. medically supported especially if doc rules it being harmful, you have better ground to say stop feeding your baby stuff that will harm her. im sure both parents didn't want harm done.
hope all goes well for you & your baby