So the only way he would have rights to "his half" of the house is if he co-signed the loan? His name is XXXXX XXXXX on the deed or title so I don't think that would be a problem.
This is not the only way. Each time your mother refinanced the property, he can claim that she essentially removed the property from separate property and moved it to marital, making it a community asset. Also, since he did not sign any sort of waiver on the property, he can attempt to claim that he has an interest in the land. The best defense your mother has is her application and intent, which some jduges can still disregard as there is no pre-nup or post-nup release denoting that the other party waived his rights to the property. My apologies on giving you such a "wishy-washy" answer, but the fact is that the ex does have a legitimate right to claim here--I do not think he will succeed mostly due to his incarceration and your mother's filing during refinancing, but he does have a valid legal argument.
I am confused where you said if there was any growth in value--does this count even though...let's say... he wasn't on any title and did not co-sign the loans?
It absolutely counts. Under CA law any assets owned while married, if they appreciate in value, the growth is split between the two parties. Some examples:
1. One spouse has a personal stock account valued at $10,000. Upon divorce the account is at $40,000. $15,000 of the growth in value is marital and has to be provided to the other spouse.
2. One spouse owns a collectible vintage auto assessed at $50,000. Upon divorce the vehicle is sold for $130,000. The $80,000 profit is split in half between the spouses.