sisters

i have 2 younger sisters aged 11 and 10 from my fathers other marriage i have not seem my sisters for 4 years as their mother and her family will not allow me or my brother to have any kind of contact with them not even to talk on the phone. we do not know why this is apart from her sepration she had with my father who i have no dealings with. please can you help me by telling me what the best way to go is to be able to see my sisters it is killing me not being able to see them my own 2 daughters have never met their aunties and they have never met their nieces. i dont have a lot of money so i need a cheap way of being able to get help with this case can you help? thank you.

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Does the father have visitation rights?