Is there anyone (like a Shoteh or Choleh) Patur from getting married & or having Children?
Clarification (sources needed): there's a Machloket if the Mitzvah of Kiddushin stands on its own or just an instrument for the Mitzvah of Pru uRvu (PuV). Ilchos Ishus by Rambam starts with Mitzvas Kiddushin and only mentions PuV at the end, while Shulchan Aruch starts with "A man is obligated to marry in order to Pru uRvu".
To rephrase your question, Can someone be exempt from Kiddushin or PuV or both.. As those are two different Mitzvos (acc to Rambam) they can be performed independently (like the two Teffilin).
- For both Mitzvos, as the Poskim did not mention explicitly who's exempt, we can infer that only Anusim are as a general rule for all Mitzvos
- As the Mitzvas Kiddushin is to actively acquire a woman (as Rambam puts it "שיקנה אותה"), and PuV is to actively "rule over" a woman, women can not perform both, and therefore women are not commanded in the first place (not exempt).
- It should be mentioned that in some extreme cases of devotion to the Torah like Simeon ben Azzai one might be considered Patur from involving in Kiddushin and PuV.