Car stayed under water

My car stayed inside flood for around 24 hrs. It was a flowing current and the water level reached a little above the number plate, and when I opened the door to escape, the water entered inside but remained at the floor level. However, as the battery in Chevy Traverse is located in the floor of the middle seating row, water stayed in the battery chamber for more than 5 days.

while I was driving in the flood, I stopped the engine of the car for a while, and when attempting to start, it always shows failed ignition. When I turn the keys to start, all dashboard panel is working fine but the engine problem sign remains yellow.

yesterday, I tried connection from a friends car's battery but it did not start. I noticed that there where fuses and plugs when opening the battery chamber. These plugs remained under water for six days. Can this be the reason!

checking the oil dipstick, it shows contamination of water, so I changed engine oil, cleaned once with washing oil, and refilled new oil as well as filter, and also the oil of gearbox.

Now the car is in it's sixth day after being out of flood but still the engine is not starting. I would like to get an idea of the actual problem. Can it be that the modules and computer of the car got problem. Please advice me how to proceed, and provide me few tips where I can rule out certain problems.