I read somewhere that the blue butterflies will spawn inside the greenhouse in the hearthfire homes. I have the bees spawning but not the butterflies. Can someone confirm this?

Yes they do. During the day times, there are monarch butterflies, blue butterlies and bees. At least in the Winstad Manor. At night times, there are torchbugs and luna moths. Sometimes, either day or night times, but especially during day times, I gather all the flying stuff, go down to the cellar to put plunder away, come back up and have to gather again. lol

EDIT. I should also say that it is usually after the 4th or 5th time that the greenhouse spawns that the butterflies show up and the same with the moths and bugs.

It took around 4 or 5 times for me, too. I read somewhere, I don't remember where, that certain butterflies spawn with certain plants. Not sure if it's true.

Do not know about that. I know that in my greenhouse I have planted

I only plant ingredients that I use, just as I only harvest stuff that I use and leave the rest.