Will someone me with questions 1 and 2 ?

1)
for a valid triangle two sides added together have to always be larger than the third
(otherwise it turns into a line)

12, 18, 6 would not be a valid triangle, because 12+6<=18
but 12, 18, 14 would be valid, because
12+18>14
12+14>18
18+14>12

2)lets start with an obvious right triangle and have the axis along the y and x axis like
so decide some x like -4 and some y like -3 and keep all other coordinates at 0:
A=(-4,0) B=(0,-3) and C=(0,0)

make it a bit more complicated (less 0s) by some x and y translation like (-2,3)
just add that to every point's coordinates and you get

A=(-6,3), B=(-2,0), C=(-2,3)