how do i set my sims i created as married

if in CAS (create a sim ) see image click on the box highlighted in red for drop down menu to select husband  or wife as the case may be then tick the tick to accept

if you have sims that got married ingame it is harder to do BUT i do have married sims ingame the wife still has her own surname but her and her husband are seen as spouse  in the relationships panel

see here http://sims4.crinrict.com/en/2014/09/change-sims-name-and-traits/       please take note of the waring on that page which states   This cheat is currently bugged and sets the relationship for children to be their parents siblings. This can’t be changed back so do not use on families