Corno basso can refer to a couple of different things.
In orchestral terms, the horns are divided into "high horns" (the 1st and 3rd parts), and the "low horns" (the 2nd and 4th horns). The reason is that, with a 5-octave range, horn players pretty much have to specialize in one part or the other, unless they are one of those rare people who can play comfortably in the whole range (in which case they generally become a soloist anyway). So "Corno basso" can refer to one of the low horns in the orchestra. By the way, the reason they don't write the two high horns as 1st and 2nd is that the notes are too close together on the staff, so it's confusing to read. Instead, they put the 4 horn parts on 2 staves, and 1 and 2 are on the top staff, with each note a comfortable distance apart, one high and one low. Then 3 and 4 are on the bottom staff, each note a comfortable distance apart, one high and one low. All visually clear.
There is also apparently an organ stop (I'm not that familiar with organs, so i speak under correction) named "corno basso". However, it's a reed stop, so it has no connection to the brass family, but there is a "corno di bassetto", or a basset horn. This is actually a clarinet in the tenor range, pitched in F, and most famously used by Mozart in a couple of operas and the Requiem. This is probably where the name for the organ stop comes from.
Context will be everything here. If there is no other horn part, and particularly a higher horn part, it is unlikely to be the brass instrument, so probably the organ stop?
As to bassotti, in strict Italian, I think it's plural for the basset hound (a dog breed), and I've never seen it as an instrument name. However, I do have an Italian violinist colleague I can ask, and our university library has instrument dictionaries, so maybe I can find it in there.
It would help to know where you got these names from.