Who was the MAIN priest in charge of the mission

It changed throughout the years. It depended on who had the duty station but it was started by Father Junipero Serra

Father-President Fermin Lasuen founded Mission Soledad in 1791, after the death of Father Junipero Serra. The Fathers that served at Mission Soledad included Father Payeras, Father Jayme, Father Ibanez and Father Sarria. Mission Soledad was so isolated, so inhospitable (weather), it had a difficult time finding priests willing to work here. All missions had a staff of two priests, except here. Turnover was a huge problem. It is reported that 30 priests were assigned here, but few were willing to stay. In 1803, Father Ibanez was assigned here and served alone for a period of 15 years, the longest resident priest. In 1818, Father Ibanez died at Mission Soledad, the only priest buried here. The last Franciscan Father Sarria refused to abandon Mission Soledad, even in its decline. It is reported that neophytes found him collapsed by the church's alter. They carried him to Mission San Antonio where he is buried (1835).