I'll try to be careful as this is not intended as a personal stab, but people fall in love "in a matter of days and weeks" all the time. Never had a fling? Their connection is amplified by the fact that there is literally no one else in the world (Mars) and they're millions of miles away from Earth.
NASA in this alternate universe is sending civilians on missions. Kelly is not military, she's a civilian and doesn't adhere to strict rules in the same way that NASA test pilots who come from a military background would. Besides, have you met US soldiers? They're famous for shagging fellow soldiers on base and locals during missions, even though it's not permitted. The Russians? Well, we know that in any universe, Russian military aren't known to be very disciplined, hence their fame for getting drunk on vodka on the battlefield – see Ukraine in present world for examples.
As for the lava tubes and water, the landing area was thoroughly mapped from orbit with ground penetrating radar in advance of the landing, as we would/will do in preparation of attempting a first landing. It was the Russians who found the liquid water. Their methods aren't known but we have already found water in our real timeline – just not liquid but the technology exists and would be deployed ahead of and during a human mission to Mars.
Regarding Danny, Ed nor anyone else was aware that Danny was responsible for the explosion. When things blew up, there was no time to assign blame and Danny headed out on his own. After that, Corrado who was the only one who knew what Danny did, was killed in the avalanche.
All of this was shown, explained or logically deduced. It just sounds like you've decided that you don't like the show and weren't paying attention.
