I don't think it is weird or shouldn't happen but, the only thing I would consider is how your ex wife would feel about that. Obviously your daughters would know how she felt about you after all those years.
There doesn't have to be a burial, those ashes can go anywhere. Meaning they can be spread somewhere meaningful to your ex-wife. If its important to your daughter to bury them in a cemetery then I would talk to her about what your ex-wife would want. If she would be ok with being buried with you, and you are ok with it, then there is defintely nothing weird about it.
This is coming from my own experience. An idea like that would not go over well with either of my parents.
I am a believer that the wishes/wants of the deceased should be followed. If you know that your loved one would never want to end up somewhere they would hate, don't put them there. That doesn't mean you have to go broke doing what they would want, but at least think of something else they would have wanted that you could do.
OP, not saying that to you, this is just a general thought.