I do not know of any reasons to think these suttas are inauthentic, but then I haven’t studied them with this in mind. If I were you, I would follow Linda’s advice and have a look at Ven. Analayo’s research. He is generally a very reliable scholar.
In general, as with all action (kamma), it is the motivation behind it that gives it its ethical significance. In other words, the act of suicide is itself ethically neutral. If someone commits suicide as an act of revenge, then this is obviously bad kamma. If, however, you are doing it because you are terminally ill and in great pain, and you are motivated by compassion for yourself (and perhaps also for others who have to deal with your situation), then I cannot see how the kamma could be bad.
There are clearly a lot of grey areas here, and I think it is better to see kamma in terms of shades of grey than as either black or white - and there is sutta support for this. So in the case of suicide, as with any action really, one should avoid the darker shades of grey and only act on the lighter ones. Total purity of action is very rare, but something to aim for as the path matures.