I have some trips coming up to Texas and Hawaii that I might be able to hit 8K spending on for new cards.

I currently have had the United Explorer with $1500 credit that just is not enough. Had it for 2-3 years and pay off in full each month.

Would I be able to apply for the Sapphire and Bold one right after the other and submit both apps in the same hour and get potentially approved (1 business + 1 personal)?

How about a combo of Sapphire and Hyatt Card (2 personal)

Lets say they reject one of them, would I still be able to get the other? Basically I would much rather take one card and get some points then get denied for one and not allow me to get the other since I could really use these.