Hello Ioco,
I wish you and your friend's family all possible strength. And I hope you find some answers quickly.
TCAS is Traffic Alert and Collision Avoidance System. The Alert word is important, because you need to know that TCAS is not just a last-ditch tool, but it also provides information to the crew to supplement their 'situational awareness'.
There are two forms of message that TCAS passes the crew, the first is Traffic Advisory(TA). In this case the system detects that there may be traffic in the vicinity which could pose a threat. However, it obviously has no knowledge of instructions passed to either it's own aircraft or any other by ATC. In this way, it maintains its independence from the rest of the ATC system, but it therefore also at times passes information to the crew which although useful, certainly would not cause or instruct the crew to deviate from their ATC instructions.
The second type of message is a Resolution Advisory (RA), in this case the system detects that the aircraft is in imminent danger of a collision. It calculates the best option to avert this collision, and gives a visual warning and an audible alert (eg 'climb, climb ') to the crew.
It is intended that this instruction from TCAS takes precedence over any instruction from ATC.
In this case it may be that a TA was passed to the crew at around the 90sec/ 1 min stage (note this is entirely speculation!!), but as I mentioned earlier, although this may give some kind of warning to the crew, they will not take any action based on this (although in reality crews very often call the controller and state that they have got a Traffic Advisory, and basically ask for some reassurance).
Not until the 15 to 25 second stage before collision will the TCAS system issue a RA to instruct the crew to take evasive action regardless of their ATC clearances.
Some news programmes I have seen tend to give the impression that TCAS is some kind of automatic flight control system which will climb or descend the aircraft without the crew's involvement. It absolutely is not. It is only a warning and instructive system.
Sincerest condolences,
Lukewarm