Is will binding - and formalizing a loan

My mother is remarried. She and my step-father both have adult children from previous marriages and owned homes upon being married. In my mother's will (date post-marriage), she willed the house to myself and my two brothers. This past weekend, she expressed concern - citing a recent discussion with my step-father, sayng he would likely not give us the house without a fight if anything ever happens to her...

Is her will binding, as her husband did not sign? Are we guaranteed the house, according to her wishes, if she is survived by her husband (who has several grown children from previous marriage)? (They do not live in the house).

Also, over the past 18 months, I have been helping my mother as she is now on disability. I have assisted with money for house repairs, mortgage notes, Insurance, land Taxes, medical and etc - as she is preparing to sell her house (which is currently vacant) to support herself while on disability. With each assistance, she has commited to pay me back for the loans - over $12K - once her house is sold (preparing to put on market this month). This past weekend, she also expressed concern with me being repaid if anything were to happen to her... How do I formalize the loans - to assure they are repaid by her estate if the house doesn't sell quickly and anything ever happens to her? Your advice is greatly appreciated.