Is a wife obligated to obey her husband by coming to him immediately upon the issuance of the visa, even if it is during Ramadan and without a wedding celebration, or should she obey her family who wish to hold a celebration after Eid?

If the husband has paid his wife's mahr (dowry), she is not permitted to refuse him without a valid excuse if he wishes to consummate the marriage. There is no objection to convincing him to postpone it for a short period, like two or three days, for her to prepare herself.