@NY718 this is the most important line of @ColeenD3 's response is in bold below. This could be very expensive if this is the case as the taxes on the social security could be much larger than the benefit ($500 credit) you'd receive
Depending on their age, one important factor is that if either collects social security, it all becomes taxable if they live together but file separately.
96% of married couples file joint because the tax laws motivate that behavior. this is a good example of that
