Well, for your first question, you would do exactly what you typed.
:If A<0 and B≥0
To get "and", "or", etc. press 2ND>MATH (TEST)>LOGIC.
As for parenthesis, do you mean something like "If (10A+2=32) and (B=6):Then"? If so, then yes you can but it's not always necessary. The calculator separates conditions based on "and" and other logic commands. You can also use "and", etc. in the condition itself. For example, "If (A=6 and B=3) or C=7" is completely valid. When you do this, though, it will check if A=6 and is B=3 first. If A is 5, the calculator will pretty much check "If (false) or C=7", so if C=7, then the entire condition will be true.
If you need me to explain further, just let me know. I don't always explain things as well as I hope I do lol.