Whoever gets there first is the winner.(用 whoever 因为是 gets 的主语）
Please feel free to bring whomever you like to the meeting.(whomever 是宾语,接 bring ）
Whosever car it is will be upset when he sees what's happened to it.
(whosever car it is = the person whose car this is)
whosever 这单词已很罕见,不宜用.