Is registering his house and car in the name of his first wife and her daughter, and giving them additional money, considered an act of differentiation and favoritism between the wives and children, and does the second wife have the right to object to that?

If a father grants a gift to his children, and then is blessed with other children, he is obligated to give them the same as he gave the first ones, based on the hadith: "Fear Allah and be just among your children." This is the madhhab of the Hanbalis. As for equality in giving between wives, beyond the obligatory maintenance, it is not necessary. The majority of jurists hold that the husband's fulfillment of his promise to the first wife is not obligatory, but rather recommended. The condition is justice between the wives. As for registering a car or house in the name of a daughter or wife, it does not constitute ownership until possession is taken. So, if the giver dies before possession is taken, the gift becomes void.