How can I know when it's time to find a home for my mom?

I figure my mom is in the last of the middle stage of Alzheimer's.  She also can't see as she has a detached retina and Macular Degeneration.  She can walk, but I have to hold her hand or she thinks she will fall.  She still eats but doesn't seem to like anything with texture.  She will spit stuff out now so it is mostly soup and ice cream.  She can still talk but is beginning to use the wrong words.  She can use the bathroom but I have to show her where it is and how to use it.  She knows me as her caregiver but she doesn't realize I'm her daughter.  My dad died last December 2007 and I've had mom 24/7 since.  I have a brother in the hospital recoverig from brain surgery (6 months now) and I have a brother who is an alcoholic, doesn't come around much and causes problems when he does.  I had to call the police on him once as he was stealing from my mom and he gets very mad and scary when he is drinking.  Now when he talks to mom on the phone he tells her how evil I am.  She won't remember but it does agitate her at the time.  I don't want to keep him from his mother but I don't trust him.  So, I have her all the time.  I hired a lady to stay with her 4 hours/day 2 days/week but then my brother caused problems and I was afraid to leave the lady there with my mom.  So, I let her go after just one week.  My problem is that I have a 12 year old daughter and a 17 year old son.  I try to stay at mom's half the time and bring her to my house half the time.  She does not know how to find the bathroom in the night and we have had some awful accidents around the house so in January I started sleeping in my daughter's room with my mom and my daughter sleeps on the couch.  I haven't spent a whole night with my husband since then.  I love mom so much and I don't want to put her in a home but I'm barely handling all this anymore.  I feel like an awful daughter just thinking about putting her somewhere else.  Plus, she doesn't know me as her daughter anymore, all I have is her trust because I'm her caregiver.  I know as soon as I put her somewhere, I will lose the only thing I have left.  I'm afraid I'll be just another stranger if I'm not the one taking care of her.  I still grieve my dad, I'm grieving my mom, my kids want me home when I"m at mom's house, I feel I"m being pulled in every which way and I don't think I can handle it anymore.  I don't mean to make this all about 'me', I hope that's not how this sounds.  I just want to do the right thing.  Any advise?