Hello,

-Each person must know how to live by themselves.

-Each person must know how to live by himself or herself.

-Every person wanted to escape from school ,but they must know it is a bad thing.

-Every person wanted to escape from school ,but he or she must know it is a bad thing.

Please help me because we know that we have to put a singular noun/pronoun after 'every, each,..etc, but I can't know whether I must write 'they or it/she/he' or not.