Ah yes, the logical middle ground between a normal mother-daughter relationship and wild freaky sex, making out indiscriminately. Science make smart! (I still find this series oddly charming...)
I find dubcon only relevant when used in a kind of tsundere sense, when the story at least implies -- and preferably outright states -- that there was internal consent. It's a fiction trope, and doesn't apply to real life. Either way, coerced sex is rape, even in fiction, even if the victim never says no. I'm glad the tags are appropriate now.