Funky; Please know I can be a very sensitive person and have also struggled with this sorta stuff; so I am saying this from a place of personal experience.
Regarding this letter you wrote did you say hurtful things towards them? Did you accuse or blame them of something? If you did, the fact that they came to see you; to a certain extent does show they care, they didn’t have to do that at all especially a 3 hour drive.
**We have to take responsibility for ourselves; not just hold others accountable and recognize our part in the condition of our relationships. Is there a chance you can push the reset button; let your family know that you appreciate them for coming to see you after you wrote them and let them know that you’re working towards healing and improving every day and that you love them and appreciate their support? Can you then leave it at that and focus on you and your well being without it being conditional or dependent on others accepting or liking it or you? You mention that you’ve raised 3 daughters as a stay at home mom; maybe now is the time to explore other opportunities, experiences, interests which will take your focus off some of this stuff? Is it possible that even after dedicating your life to your daughters they choose to side with others or not speak to you; that you may be letting your feelings about your family disrupt your relationship with them? Perhaps try not saying anything negative or unkind about your extended family to them; sometimes people can feel put in the middle because they are hearing you say hurtful things towards someone they care about or they feel like you’re making them choose between them and you; maybe to you it seems their siding with other family but it is just that they don’t agree with your approach, view or attitude about the situation. Seems like you raised them to be their own person so you can’t always expect like mindedness from them always. Accept/Know and Love them your family for who or what they are and I believe they’ll eventually do the same. Everyone has problems, most that we never can imagine let’s not make ours their responsibility too, we have to find the right person, place and time to work out our issues and sometimes it takes going to someone that doesn’t know us from a hole in the wall to give an impartial perspective, see a counselor but also fill your mind and time with positive, constructive pursuits. *Take a vacation with your husband; Disney in my opinion is expensive, boring and tiring.