Factory reset or use our apple id

Do you know his Apple ID and password? If not, you can't fully utilize the device because at some point it will ask you for that information. For information about how to request access to a deceased family member's Apple accounts, and through this their equipment, click here --> How to request access to a deceased family member's Apple account - Apple Support

As for whether or not you ultimately erase it, you need to decide that. If you sign out of his account and sign in with yours it will ask you if you want to keep and combine information from both accounts. In some cases people want to do this for keeping things like photos. However, this can also result in some undesired mixing. Unless you're in that position you should probably just do as instructed in this article --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

After you do the things in that earlier about what to do when you are giving away a device, it will be as if the ipad is brand new. Your husband can then set it up for his use. Read the support article titled: 'Set up your iPhone, iPad, or iPod touch'. Click here--> Set up your iPhone or iPad - Apple Support

The SIM card is only used to store phone service settings from your telephone service provider. You can leave it in if you want to continue the service.

After you erase it, it will be like brand new. It needs to be set up completely. Do not delete the emails first, simply erase the entire device. If you delete them first then iCloud may assume you wish to delete them everywhere. Erasing the entire device just remove things from that device.

Reset the device as outlined in the second link. What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support