I'm pretty sure most of what you are suggesting is already possible, at least to a degree. You can influence Mr/Mrs. Maywood's marriage in a few ways such as revealing or not revealing his cheating ways. At the wedding you can further distance them or try to mend their relationship etc.
As for Kyle/Heather/Nikki, you can get them all into a harem together, but I think you have to transform Kyle first. Then go on the movie date on Monday evening and there's a Kylie girlfriend option which might add her to your harem as well as Heather and Nikki which should already be a part of it assuming you did so earlier or green light them in class.
The talk to Kayla option might be important later on when there's more content, but it makes sense that you can totally ignore it. It makes Kayla an ally and a lover. Having Kayla in an upcoming battle might be useful, but my guess is that if you have a contract for her it's not going to matter much.