However despite giving all these options it then does as you say draw the tree with one line coming down from the two parents, this surely has to be right. Where they are not being helpful is in not using different types of lines to indicate different relationships. then again does it really matter if the parents are married or not they are still just as much biological parents whether they are married or not, and then of course not all married couples are the true biological parents of their supposed offspring. Oh dear its all getting complicated ....
My bold emphasis.
But that was the whole point of the OPs post. (as I understand it)
She wanted to denote the separate parents in her tree
and to be able to see them at a glance as not married, without having to go into the minutiae of facts.
Added:- MyHeritage Family Tree Builder (on PC) is better in this regard as it has a box between the couple and their children in which one can state the relationship and it is easily visible but only for the main couple, other couples are shown with a ring between them until they take centre stage. The other problem is that only 5 generations can be seen on screen at a time, which is one reason I hardly use it now.
I'm not sure about the on-line version as it is sometime since I visited the site. edit:- just visited the MH site and it shows a broken line between divorced and separated couples but doesn't distinguish between any other relationship and there is no relationship box easily visible as on the PC version.