I've recommended Qured on this site. Our friends recently ordered from them and didn't receive their testing kits, even after calling and being reassured they would get them the next day. So after 6 days they cancelled and had to scramble to find another alternative. If you do order from them, be sure to order well in advance.
Use the discount code AATRAVEL15 or BATRAVEL15 to get a 15% discount which brings to price to £33.
Someone on this site recently successfully used C19testing.co.uk for a £29 antigen test. You take the test at home and email the result. There's no video call.
https://www.c19testing.co.uk/rapidtravelUS requires the test to be taken within 3 days of the flight to the US. So if the flight is on a Thursday, the test could be taken starting on Monday. I would do the test 2 days before the flight. If the flight is delayed by a day the test is still valid, and if there's a problem with taking the test or getting the result, you have another day to sort it out.
I hope you enjoy your visit with your in-laws.