You can stop the Farsi club.
You can offer to meet her friends from there in the park or at a play centre or anywhere else instead (not as well as the club, I'd stop that immediately) and gradually break away from them if you want. But I would stop the club right now.
You could do it easily, by being busy with something else, and not telling her that she's not going again. Yes it is Farsi club tonight but this is the only night X could come to play. No, we're missing Farsi club today because we've been invited out with X. We are going out for dinner today and won't be back in time for Farsi club.
Children are surprisingly resilient and make new friends more easily at five, so why not just stop the Farsi club and offer her the chance to go somewhere else. Dancing, swimming, another language club, anything else where she can meet other friends and have fun.
And as everyone else has said, definitely do not take them to Iran or anywhere else to meet up with him. He can come here, but don't have him stay with you in your home or think for one minute that because the passports are with your parents he can't take them out of the country.
There are ways and means of doing anything and he might be able to use the passports of other children in the family, or apply for passports for your girls on his own, either here or in Iran.
I've read about children being taken by fathers who still then have little to do with them, handing them over to female relatives to raise and leaving them isolated from both parents in a strange country with little chance of being returned to their mother.
There was a recent thread on here about this happening to a British woman who had an American ex-partner wanting her to give birth to their child in America, so it can happen anywhere.
Please get proper advice and be as careful as you can be.