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Really, the only way is to be diligent about digging them up. Remove any flowers that the remaining ones produce to keep seeds from spreading and when you dig them up, make sure you have gotten all of the bulblets that were attached to the mother bulb. You can spot treat with Round-Up or boiling water but be aware that both herbicides will kill any plant material it touches, such as surrounding grass or plants that it splashes on.

Yes, you can divide and transplant them just about any time, depending on your location. Grape hyacinths are quite hardy and take transplanting well as long as you provide the proper growing conditions and care. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/grape-hyacinth/planting-and-care-of-grape-hyacinths.htm You can minimize their spread by removing the foliage and any seed pods. This will keep seeds from being spread and weaken the bulbs so they cant produce bulblets.

It is very easy. Just spread the seeds out over the area that you would like for them to grow. Keep the area moist and clear of debris. It may take a few years before they get to blooming maturity, though. Just so you are aware.

Yes, they should be fine under pines. Look for varieties that are hardy in your area. This article has information on growing hyacinth: https://www.gardeningknowhow.com/ornamental/bulbs/grape-hyacinth/planting-and-care-of-grape-hyacinths.htm

It is not unusual for these plants to sprout now, as they tend to enjoy cooler weather. Of course, they will die down once it freezes but will return in spring.