OP, from the little you have said about your marriage, it could be suggested you may be a quite passive person. If your husband is absent from you all for 9 months of the year and you are entirely dependent on him for money and family decision making, eg he doesn’t like the counselling idea, then you are in a pretty much impossible position.
He isn’t there to know what’s going on and yet you abide by his decisions and rely on his provision. Are you prevented from parenting as you would wish to at all ?
Could this be connected to why things are going wrong for DD2. ?
Your daughter doesn’t appear to have an effective authority figure in the home. She is easily able to say ‘I don’t care’ because may be to her, her own father appears not to care and she gets away with everything so easily with her mum and older sister.
That isn’t a good feeling for her at all, poor girl, and I wonder if it comes from not feeling the safety and security of firm and confident guidance / boundaries where they are needed now, - and when they were needed in earlier childhood.
Is DD1 able to assert herself strongly at all?
Does she not give her younger sister a massive row when she realises her stuff has been stolen and messed with and does she not put her own strategies in place to protect her stuff?
Is it possible that DD2 is learning to assert herself (good for her) but in the wrong way because she hasn’t had assertiveness demonstrated for her in the family. She is floundering about, trying to find her way. She needs lots of examples by way of family debate and discussion as well as by way of role-modelling of family values.
It appears that you are a single mum for most of the year yet unable to parent effectively because you are beholden to an absent husband who does can do little proper and active, face to face parenting.
Could it be you are sometimes waiting for him to make decisions or waiting for him come home and sort things out and for things to get back to normal? Meanwhile, ‘normal’ never really happens and problems are left to solve themselves. Is this any where near the situation OP and is it unsatisfactory to you in any way?
I see you have now further commented that you are happy with him and the situation so may I have the wrong end of the stick entirely. But I think it’s still worth thinking about.
I kindly suggest that you could have a real heart to heart with your two Dds where you could all speak your true feelings in turn. You first. Take the lead with confidence and be really honest. You could explain exactly how you feel and how and why you are struggling. Acknowledge the unusual marriage arrangement openly and let your girls see that although it is far from ideal for any of you in some respects, you will still protect your own self respect, as well as theirs, by not accepting any more abuse within the home, eg verbal abuse and allowing stealing. And they should both do the same. Talk about it a lot without pointing the finger all the time at DD2.
Let the girls talk and agree that you all need to stand together and support each other.
I do think you need to get to the root of what is going wrong for DD2 rather than by just treating the symptoms. I feel for you doing it largely on your own. Good luck!