I’m terribly, terribly sorry you find yourself in this situation. I don’t know if your kids are completely thoughtless or hostile.
I do know that you won’t get very far talking to them about the dogs. What needs to be talked about is your relationship with each kid and what they imagine your role should be in their adult lives.
I hope you will consider making a “date” with each of your kids to talk about that. Deal with them separately, not as a group, so you can get to some depth in your discussion. Try to leave your upset and justifiable anger at the door. Instead, be curious and loving. Let them know that you are open to hearing what they have to say. Tell them how sad it makes you feel to be unable to go to their homes and to feel like they are disappearing from your life. See if they have any suggestions for what they and you can do differently to maintain a relationship.
If you are uncertain about how to manage such conversations, I urge you to see a therapist for a few sessions to help you know what to say and how to say it. The support a therapist can offer may also give you some additional strength.
I wish you well.