Holy fiddle sticks, you are all a bunch of angry, nasty people with their ugly judgy pants wadded way too far up their behinds!
Anyone who argued that not wearing a seatbelt is ok because most of us grew up in a generation that did not have strict seatbelt laws and most of us survived MUST have hit their heads from lack of seatbelt use......you do understand that are current laws evolved from what they were then to what they are now because of the FATALITIES that resulted from our crummy old seatbelt laws.
Everyone riding in the car should have their own, individual seatbelt. If there aren't enough seatbelts they shouldn't be in the car.
You asked your ex to make sure your younger son was in a booster seat and he did, great. Just because there is not a law requiring someone to do something doesn't mean it is safe or a good idea......cigarettes are legal to smoke, does that make it a good idea?
You ex is responsible for his foster daughters well being, if he is not doing it to the best of his ability then he should be reported. I called CPS on my godsons mother because even though she had a mini van that offered a seatbelt for all 4 of her children she consistently drove everywhere, short and long distances, with none of them buckled in to the regular seatbelt let alone car seats.....the youngest is only 2, the oldest 6, they should have ALL been in car seats or boosters.
Talk to your attorney and see if what he is doing (or not doing) with his foster child and see if your attorney feels it has any bearing on your case. He is putting your children at risk.
Next, call CPS and report him anonymously. Do not feel bad for doing the right thing to keep all the children involved safe.