the warning means what it says

the total weight for the vertex will not be a whole number

you vertex is being influenced by two bones and each bone gives a weight on the vertex, the way soft skinning works is that movement of the vertex depends on the weight assigned to the influencing bones

so for example you can have the weight be 0.43 on one bone (one column in that table) and the other bone would have to be 0.57, and they total 1

i've never used what you're doing to adjust weights so im not sure how to change the values in both columns at once (although i thought it was automatic? obviously not)
i always just used the paint weights tool