When parents say no there might be some reason to say no.
Sometimes parents without any reason say no because whey guy get married he only listens and believes to the girl and not to the family. That scare them and they don’t want to lose their son.
If istikhara is good then you guys can go for it. If any or both of them are not good for each other then Allah will help you.
It’s your responsibility to have a balance between your mom, sisters and wife.
No matter you marry the girl you love or your moms pasand there will be problems between 2 of them as it’s going on from sadiaan (many years).
If anyone starts anything wrong then there are problem. It’s your responsiblity to find out truth if any problem is there and do good to correct the mis understanding and do Imaandari no baymaani with anyone. Allah will help you.