Can lower blepharoplasty with fat transfer to midface/cheeks be done before double jaw surgery?

I think that you should seek out the treatment that addresses your concerns. The timing is not really essential. Most procedures can be performed in any order. As far as jaw surgery, an underbite doesn't necessarily require treatment if your functional ability to chew is unaffected. If you want to address the cosmetic aspect of an underbite, just have a chin implant or genioplasty. Many of my patients don't want to undergo a surgery that requires a long recovery.

You are correct. Maxillary surgery can change the midface. Because if this, I would have an evaluation for your jaw problem. If any surgery needs to be done on the maxilla, I would postpone any blepharoplasty or midface treatment until after the maxilla heals.