While looking for a bigger place to live, do I have to add myself to my grandma's lease while staying at her apartment?

DonnaJay, you would be living with your Grandmother as a sub-tenant, more so than a Caregiver, since you are looking for some place else to live, please check with the landlord or with the apartment management to see what is required.

If your Grandmother is living in a senior facility, there might be extra rules and extra payments regarding this.

If you are planning to move in and live with your grandmother, then I would have thought you do have to, yes; because your landlord needs to know who is occupying his property. Is it going to be a problem?

One thing to consider is whether a landlord would agree to a lease with someone of 104 years. You might have to countersign as well if your GM isn't able to understand the terms of the lease. It may all depend on whether the apartment is in a complex or a privately owned and operated facility.