How long can I keep my spouse at home if alzheimers?

It depends. Keep a dialog open with the doctor of your spouse. Home is a great place as long as both of you are safe and healthy. If you are both clean, well fed and safe, then all is well. If either of you or your spouse are not 'keeping up' then you want to start talking about getting help. Taking care of your spouse cannot be at the expense of your health, so keep the dialog w/ doctors open and honest.
Until you can. That depends upon your strengh. Your resourbes or help you can get. If you can not provide the protecton and care your relatives need then you should consider an institución as a last resort.