We understand your concerns and we are here to pray with you and provide biblical encouragement.
Firstly, we commend you for praying for your son's academic success. Remember the scripture in Psalm 127:3, "Behold, children are a heritage of Yahweh. The fruit of the womb is his reward." It is wonderful to see you are encouraging his education.
Let us pray:
Dear Heavenly Father,
We come before you in the name of Jesus, lifting up this family. Lord, we ask that you grant success to their son as he takes his test today. Guide his thoughts and help him to recall all the information he needs. We also ask that you bring clarity to the situation with his math assignment, and that the teacher will be fair and just in their grading.
Father, we also lift up their transportation needs. We know that you are a provider and that you care about every detail of our lives. Guide them to the right solution, whether it is repairing their current car or finding a new one. Give them wisdom and discernment as they make these decisions.
Lord, we also pray for the health and well-being of their mother-in-law. Comfort her and let her feel your presence until they can be reunited.
In all these things, Lord, we ask for your will to be done. Help them to trust in you, even in the midst of uncertainty. We ask this all in Jesus' name, for it is in his name that we have access to you. As the Bible says in Acts 4:12, "There is salvation in none other, for neither is there any other name under heaven, that is given among men, by which we must be saved."
Amen.
Regarding your situation with the car, consider these verses:
Matthew 6:25-26, "Therefore, I tell you, don't be anxious for your life: what you will eat, or what you will drink; nor yet for your body, what you will wear. Isn't life more than food, and the body more than clothing? See the birds of the sky, that they don't sow, neither do they reap, nor gather into barns. Your heavenly Father feeds them. Aren't you of much more value than they?"
Trust that God will provide for your needs, just as he provides for the birds of the sky.
Finally, we want to encourage you to continue to pray in the name of Jesus. It is by his name that we have access to the Father and it is by his name that we are saved. If you have not already, consider the message of salvation found in John 3:16, "For God so loved the world, that he gave his one and only Son, that whoever believes in him should not perish, but have eternal life."
We are here for you, joining our hearts together in prayer. Keep trusting in the Lord, for he is faithful to provide.
Prayer Focus: God, Thank You. Thank You for loving me. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, mind, soul, body, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
