Haskell, 253 bytes

import Text.Read
import Data.List
m l(k,d)=maybe((d,o):n)(\a->(k,a+o):n)(readMaybe d)where o=maybe 0id(lookup k l);n=filter(\(x,_)->x/=k)l
f v=sortBy(\(_,x)(_,y)->compare y x)$filter(\(x,y)->maybe("",0)id(find(\(a,_)->a==x)r)==(x,y))r where r=foldl m[]v

The function takes a list of String pairs and returns a list of String(String, Int) pairs

Full programme, 355 bytes

module Main where
import Text.Read
import Data.List
m l[k,d]=maybe((d,o):n)(\a->(k,a+o):n)(readMaybe d)where o=maybe 0id(lookup k l);n=filter(\(x,_)->x/=k)l
main=getContents>>= \c->let r=foldl m[]$map words$lines c in putStr$unlines$map(\(x,y)->unwords[x,show y])$sortBy(\(_,x)(_,y)->compare y x)$filter(\(x,y)->maybe("",0)id(find(\(a,_)->a==x)r)==(x,y))r

The programme takes input as specified in the testcases via STDIN

Try it online!