Reminding ones household that Shabbos is near:
Slightly prior to sunset, one is to caution his household that they should light the candles and cease from doing any forbidden work. Likewise, if one’s wife baked Challah [as is required due to the custom] then slightly prior to sunset it is [an obligation in Eretz Yisrael, and even] in the Diaspora, it is good, to ask her if Challah was removed. If one is not at home at this time then he must [call or] send a messenger to remind his household of the above.
How to speak to ones wife and kids: The above reminders and questions must be said in a soft tone in order so they accept his words.
 However one is not to hurry and remind his family while there is still much time left during the day, as they will not adhere to the reminder, as they will assure themselves that there is still plenty of time remaining. [ibid]
 Ketzos Hashulchan 73 footnote 10, as in Eretz Yisrael one may not eat bread if one did not separate Challah from it before Shabbos. Thus it is an obligation. However in the Diaspora being that one may still eat bread even if one did not separate Challah from it before Shabbos, as will be explained in the coming footnotes, it therefore is not an obligation to ask one’s wife if she separated Challah but is merely a good thing to do.
 But not an obligation.
 As Challah may not be removed on Shabbos. (Now although in the Diaspora from the letter of the law one may eat un-tithed bread so long as he leaves over some bread which he will remove the Challah from later on, [and thus the above reminder should not be needed in the Diaspora], nevertheless initially the custom is to remove Challah before eating the bread due to suspicion that one may come to forget to remove later on, and in retrospect it happened that he ate Tevel.) [Ibid] The M”B [260/13] however concludes that today the custom is no longer to ask if the Challah was removed.
Asking if the food was tithed in Eretz Yisrael: From the letter of the law in Eretz Yisrael it is also necessary for one to ask his wife if she removed the tithes from the other produce needed for Shabbos. [ibid] Nevertheless today being that the Kashrus organizations deal with these separations, this question is irrelevant. [Ketzos Hashulchan 73 footnote 9]
Asking on Eiruv Chatzeiros: Likewise it was required back then to ask if Eiruv Chatzeirus has been done, however being that today this Eiruv is done once a year on Erev Pesach, there is no longer any need to ask. [ibid]
 The Magen Avraham 260/2 writes that one is to speak softly being it is forbidden to enter too much fear into one’s household. This itself is due to that if they fear the father too much they may come to lead him to transgress eating a forbidden food, or that they themselves will transgress Shabbos due to fear of not serving him his needs promptly.