The Istikhara binds or guides the person who did it not others. It can be possible that the parents want guidance on the future of a proposed marriage through Istikhara, but that is for them.
The Istikhara done by a person does not bind other person even if they are husband and wife unless it was done by request from the husband and his wife was just doing it on his behalf and on his intention.
To answer your question, yes it is possible for a dua to change a given situation. With that said, i would caution against overuse of Istikharas. They should only be performed after one has utilized their intellect to the full extent, and they have consulted with others, and done everything within their reach to reach a solid conclusion. If they still haven't been able to reach a conclusion, only then should an Istikhara be utilized.
In some cultures in the Middle East, Istikharas are over utilized while God has given us an intellect for a reason....
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