Trying for 50/50 Custody 35/65 Agreement Since Sept

My question involves a child custody case from the State of: California

My fiance and I are trying to get temporary full physical custody of his daughter and would eventually like 50/50 custody. The girl and her mom were in Mexico until March of this year. My fiance and his wife were no longer together but there were residency papers pending with the mom and he wanted to make sure the mom could come back legally so that the little girl (three and a half years old at the time, now four and a half) had both parents.

When the mom came back, she and the little girl stayed in a room at her sister, "M's" house. My fiance would go to see the little girl every day and after a month or so would pick her up and keep her until bedtime. By May, the little girl was staying in our home for several nights at a time and with the Mom's consent, we put the little girl in preschool for a few days a week so that she could start learning English.

The little girls mom has been extremely difficult. She would agree to let my fiance pick up the little girl, then wait until he drove over to the house and, in front of the little girl, would say that they had something come up so he would need to pick her up the next day. Finally, she called the police and said that he'd kidnapped her (completely ridiculous, she was with us, the mom knew and had verbally consented to having the little girl be with us and as soon as the police called my fiance, he brought the little girl back only because we didn't have a court order).

Needless to say, we were in court the next day. My fiance and the girl's mom went to mediation and the mediator told him that he wasn't going to get primary physical custody or even 50/50 so the only way he could ensure that his daughter wasn't taken out of the country and that he did have time to spend with her was to decide on some kind of visitation. He agreed to Friday night at 7pm until Monday to school. He verbally agreed to drop off the daughter to her mom on Monday at 7:45 am because she was attending a school where she had to be there very early.

That was Aug 26, 2008. Since then, the mom has had a baby and moved into her other sister's one bedroom apartment where there are a total of eight people living. The little girl had been complaining of abuse. The mom has completely denied it, but we filed a complaint with Social Services who explained to the mom that hitting a four year old, especially with shoes or other options, isn't the best way to decipline. Since that time, the little girl hasn't mentioned being hit (Thank God!!). The little girl also stated that when she goes places with her mom, she sits on a pillow between the two front seats of the car because all the other seats are taken. The mom didn't confirm this but did state that she wouldn't agree to only transporting the little girl in a car seat in an insured vehicle driven by a lisenced driver because 'you know very well that my brother in law drives us around and he doesn't have a driver's lisence.'

We are asking for temporary full custody until the mom can provide the little girl with a bed in a bedroom and can agree to only safe and legal methods of transportation. We are also asking that a 'no corporal punishment' order be added. My fiance has actively tried to work with the mom, going as far as to offer on paper to give her money for first month and deposit on an apartment. Her response is to say that she's not giving up nights with her daughter because she likes having her around and if he wins, she isn't going to deal with seeing her daughter only during the day. She'd rather just leave her daughter and go back to Mexico.

What are our chances of getting this order granted?? We aren't trying to take the child away from her mom, we are just wanting to make sure she is safe until the mom has the means to tak care of her.