Changing owner info on iPhone XR

This sounds like you are going to run into a Activation Lock, you need her Apple ID username and password. Normally there is no way to get around activation lock without the original owners username and password, but Apple may be able to help you with this since the phone belonged to a recently deceased spouse. You should contact Apple: Contact - How to Contact Us - Apple

What does “without losing the other data” mean?

This iPhone belonged to someone else. Now you’re trying to take it over. The iPhone should be thoroughly and completely cleansed to “like new” software-wise before you “move in” using your credentials.

Here’s how to do that cleansing.

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Typically, when setting up an iPhone (new or used,) you want to do so with your Apple ID. By using iCloud, are you saying that you restored your data from an iPhone backup?

Unfortunately, there is no way to transfer data between ID ... if that is what you are asking.

First of all:

How to request access to a deceased family member's Apple account - Apple Support

Next, you may consider:

Set up Family Sharing - Apple Support

I want to change the default owner of this iPad on iTunes