Wifi keeps disconnecting on iPad and older MacBook Pro

We have a reasonably recent iPad Air and an older (Mid 2012) MacBook Pro that keep disconnecting from the wifi. My own devices all connect just fine, it's only my husband's devices that cut in and out.

We can sometimes reconnect by just shutting off the wifi (on the device) and turning it back on. We usually have to input the password again or share it from another person's device.

Other times, we get an error message while the MacBook is trying to connect that says "Wi-Fi does not have an IP address and cannot connect to the internet" or it says the password I used is invalid despite the fact that it IS correct.

I deleted the networks and tried connecting again. As it tries to connect, it says Wifi has self-assigned IP address (insert long list of numbers and letters) and will not be able to connect to the internet. Sometimes, it just keeps trying and eventually connects to the proper IP address.

I've tried a number of different suggestions I've found in this community but nothing sticks. Most of the others with the same problem have a newer MacBook.

Any suggestions?