Do Catholics Recognize Second Eastern Orthodox Marriages as Valid?

It is my understanding that the Eastern Orthodox can get married a second time after a separation when their first wife is still living. It is also my understanding that Catholics do not permit this in the Catholic Church. I also believe Catholics recognize Orthodox first marriages as both valid marriages and valid sacraments. Assuming all of the foregoing is accurate, how do Catholics view Eastern Orthodox second marriages? Valid as both a marriage and a sacrament? Invalid for both? Some other thing? For example, if that couple wanted to convert to Catholicism, would the Church accept them as married?