Yerushalmit: What do you mean take over the time schedule? I leave for shul when I normally do whether my SIL is ready or not. (BTW, my shver A”H never waited for me to go to shul as I generally went to shul earlier then him). If he decides to daven in another shul, I wait to make kiddush a reasonable amount of time just like I wait for my sons (both Leil Shabbos and Shabbos morning). If he does not arrive within a reasonable time (and the same for my sons) I make kiddush and he has to make his own. He holds 72 minutes after shkiah and generally says V’yiten Lchah before havdala. If i arrive home from maariv earlier then 72 minutes, I wait for him.
My SIL has not “demanded” anything so I am not sure how i would react if he did. I doubt he will since he seems to take after his father and I have found that he is not a demanding person.