I am not a home owner. So if I can claim the property taxes for his house, how do I navigate your prompts to do so when I file?
Only the owner can deduct the taxes and interest.
If you are the "constructive or beneficial owner", you can deduct the taxes and interest even if you aren't the legal owner. "Constructive ownership" is a complicated concept but in general it means that you treat the home as if you owned; that you accept all the responsibility of ownership and derive the benefits of ownership.
For example, it might be the case that you are the only heir, and will inherit the house as soon as the estate is probated, at which point you will sell it and keep the profits. In the mean time, you have been paying the tax, mortgage, and performing all needed repairs and maintenance to keep the property in good shape. You might be a constructive owner in that case.
On the other hand, if the home will be inherited by someone else, and you are paying the bills but not doing any other work, and the heir is starting to move their stuff in, then you probably aren't a constructive or beneficial owner. In that case, the estate should be making the payments and deducting the expenses on the estate tax return, or the estate should reimburse you before the remaining funds are disbursed.