You are sooo close. Try this.
var sVal = getField("ar_first_name_2").valueAsString;
if (sval != "") {
getField("ar_last_name_2").required = true;
getField("ar_title_position_2").required = true;
getField("ar_dob_2").required = true;
getField("ar_address_2").required = true;
getField("ar_city_2").required = true;
getField("ar_state_2").required = true;
getField("ar_postalcode_2").required = true;
}
Actually, you should use this code, so that required is turned off if the user deletes the first name.
This code is placed in a custom, format or validation script.
var bReq = (event.value != "");
getField("ar_last_name_2").required = bReq;
getField("ar_title_position_2").required = bReq;
getField("ar_dob_2").required = bReq;
...etc...
And since all the lines required the same code. I'd generalize the code into a document level function. This reduces human error when copying the code to all the different lines and makes it much easier to change the code.