If they are searching for emunah in Hashem, they definitely should continue keeping the mitzvos.
It depends. If they truly want to believe in Hashem then they should listen to proofs from our side. Rabbi Orlofsky and Rabbi Lawrence Leib Keleman have some great shiurim on proving Hashem and the Torah, you can find them on torahanytime.
If someone doesn’t want to believe, then no one anyone says will convince them of anything.