I'm sorry to hear about all the drama you have to deal with. You would think that being disfellowshipped and completely ignored by your family you would at least be sheltered from the drama. But, it's not so.
I think it's kind of you and your husband to consider loaning them money, especially after the way they've treated you and your son. There must be a lot of pressure that not giving them the money they need will make them view you even worse than they do already. That sucks. My fear would be that giving them the money won't change how they feel about you even one iota and that once you do it this time you have set the precedent and you will be doing it again, even if you right now you say it's a one time thing.
Best of luck.