My Dad passed away and he was cremated. Who has the right to determine how the ashes are handled?

When my father passed a few years ago, he was cremated. My mother survives him, as well as 5 grown children. My mother was not sure if she wanted to be cremated, so we waited to bury my dad in a Veterans Cemetery until she determined what she wanted to do. In the interim, my brother (who was an absentee son) has held the ashes 3 hours away. My mother decided to be cremated and both my mother and I requested that the ashes be returned so that my father could be interred. There have been numerous issues within the family by way of squabbling and there's always somebody not talking to the other. As a result of this, my mother wanted to be sure that when she passed, she knew she would be side by side with my father. So, she asked that we make those arrangements with the Veterans Cemetery, which I did. However, my 3 out-of-town siblings refuse to honor my mother's request and my brother refuses to release the ashes. The other two siblings think that we are dishonoring my father by treating him like a "football", being passed around. I support my mothers request. She lives with me and I know that this bothers her. She fears that she won't be buried with my father. So now, the family has shut down and no longer communicates at all. My father sits on my brother's mantle.....my mother who is now 80 wonders how this is going to all shake out because she cannot be buried in the Veterans cemetery without my father being in there too. I feel my siblings are being vengeful for past issues with my mother and are trying to show their "loyalty" to their father. Ironically, you could count on on hand the number of times they visited in the last 5 years of his life. I can let it go and my mother kind of has too, but am I dishonoring my father by not acting more pro-actively trying to get him buried, like he wanted to be.