Hey there! Glad to hear you’re enjoying the game.
Regarding Hitomi, there is a bug, but it's not the house disappearing bug. If you choose to send her to the hospital, her house will indeed disappear. However, if you send her at the second visit, an event will trigger at the end of the month. The bug is that after sending her at the first visit, the hint for Visit 2 shouldn't appear, but it does.
As for Syllia, she currently has around 4 small events for heart 1 and another 4 for heart 2, similar to Hitomi. You can unlock heart 2 for Syllia when pass month 3.