Upsetting a 14 year old girl that has just lost her mum... yes my husband does not want to do that
Not "upsetting" a non-resident teenage child is a common motivation for many fathers - I'll hazard a guess that the reason your DH and his DD have maintained their relationship up until her mums death despite high conflict between the households is because your DH has taken the path of least resistance - fearing that his DD will "opt out" of contact if he upsets her?
Unfortunately, your DH is no longer the NRP, he is his DDs ONLY parent, and there is no magic solution to the situation. Your DH has a legal, and moral, responsibility to protect his DD - regardless of her feelings or opinion of his actions. Action or inaction will upset her - the only difference is when the consequences will manifest themselves. Leaving her where she is now only delays the damage and hurt it causes her.
Your DSD stepfathers actions are misguided at best and abusive at worst. Who knows what is going through his mind? Are there cultural obligations that your DSD will be expected to fulfil - for instance, becoming homemaker and carer for the younger DCs and her stepdad?
If your DH is unwilling to act, then I fear he will lose his DD. I just hope that she has the opportunity for love and happiness rather than abuse and misery.
Oh and the court will award PR regardless of my husband's opinion on the matter.
If you know this to be the case as a matter of fact - despite precedent and legal guidance - then there is a great deal more to the circumstances than you have shared on this thread. Courts do not award stepparents with PR of their stepchildren against the wishes of parents unless the parent is unsuitable.