Do babies with fused bones in their skull need surgery?

Yes. Premature fusion of the skull bones in an infant will not allow the skull and brain to grow normally and will lead to disfigurement. Surgical correction can range from something as simple as opening the line of fusion to a complex reconstruction.
Craniosynostosis. They often require surgery to allow the skull to grow. A board certified craniofacial plastic surgeon would be the doctor to speak to.
Yes. If skull bones are fused, it's called craniosynostosis. It needs to be separated in order for the brain to grow.
Sometimes. Seek a consultation form a craniofacial plastic surgeon.
Yes. There are many growth lines in the baby skull that push apart from each other in normal growth. If a major line fuses early, a progressive skull deformity may result & surgery may be needed. Most unusual skull shapes today are due to sleeping position & improve with age. If your feel hard ridges where the suture lines join you need to see your doctor. If referral is needed tests will confirm it.
Possibly. Craniosynostosis are associated with several syndromes. The baby would need to be evaluated by their pediatrician and surgeon to determine need and timing of surgeries.
No. This answer depends on the amount of fusion, the location, and the bones involved. There are some genetic disorders that lend to large fusions, creating very abnormal skulls. Crouzon's disease is one such disorder. If fusion is detected or found on imaging, immediate follow up with a neurosurgeon and geneticist is required to help make that decision.