Q: Can I replace crankshaft sensors on my own and where can I get a schematic/video?

My forte has sporadic problems starting - sometimes I have to turn key a few times to start. One time it shut off on me while I was driving and I had to restart it. Once it wouldn't start even tried to have the battery jumped. Then after several attempts/waiting attempted one more time and it started right up. Replaced battery then. 2 wks ago left work and car would crank but not start. I asked for a jump from security. They tried using their big unit no luck then tried jumper cables no luck. Husband tried his big unit no luck and we towed it to a shop. Diagnostic at shop said I needed crankshaft sensors replaced but when they replaced those, car still wouldn't start and after more research they said ECM unit needed replaced for $1,800 (now think jumper cables fried ECM). Too much so I replaced with used ECM but car still cranks won't start. How hard is it to replace the crankshaft sensors myself and how likely that this is real issue now? Shop put back in the old sensors I think.

My car has 127000 miles.
My car has an automatic transmission.