Okay, so you can either use different oils in each vehicle or use the same oil. You don't want to use different oils so the question becomes using a 0w-20 in both, or a 5w-20 in both.
I'd say to use M1 0w-20 in both, and keep your receipts and records organized in the very rare chance you ever need to use them.
Here's my reasoning for that: Mobil says you can use 0w-20 anywhere 5w-20 is called for, Mobil also has an excellent warranty any time you're using an M1 product and the issue can be traced to their product. So let's say there's something major with the Kia's engine that needs to be repaired under warranty, Kia then asks for your records to prove oil changes and routine maintenance was done. You have you records available and give them a copy of them. One of two things then happens, 1) they repair it under warranty, or 2) they try to deny it because a 0w oil was used. Obviously the first one is ideal, but let's say the second one happens. They will have to show how using a 0w oil caused the problem. Proving the 0w oil caused the problem means the item is covered under the M1 warranty, so you can recoup the cost of the repairs from Mobil because you've always used M1 and no other oil can be blamed.
However, this all works in theory, in real life it's probably a nightmare jumping through all the hoops to get either one of them to acknowledge it should be repaired under their warranty.
So this leaves you with deciding if you want the mild inconvenience of keeping track of two different oil types during the course of the warranty periods. Or a major inconvenience that occurs only once in the extremely unlikely event that a major warranty repair needs to be done on the Kia (since I suggest using 0w-20, you don't have to worry about the Honda warranty).
If this were my vehicle, I'd use M1 0w-20 for the reason stated above. You may decided otherwise based on what you're comfortable with.