Regarding modesty in terms of relations: The woman has gone to the mikva on the proper night, however your in laws are visiting or you have guests visiting. Should the couple postpone relations due to modesty because theres someone else in your home. Nobody else knows its your mikva night besides the couple.
It is better not to postpone marital relations, but if it will not be comfortable for one or both of the couple, then it is permitted to postpone. Please see http://www.dinonline.org/2011/08/15/posponing-mikva-because-of-tzenius/ and http://www.dinonline.org/2011/08/15/delaying-mikva-2/ for further details (the same rationale as postponing immersion in the mikva applies to postoning actual relations).