Such an adorable boy! What kind of tools are you using? A good comb can help make a difference. My favorite is the Chris Christensen face and leg buttercomb. There is also a Madan one that Mimimomo, Jenny, sells on her site
toplinepet.com
Use treats, cheerful encouragement, some massage, and lots of patience. Try working when he tired and relaxed, or tie grooming to a favorite activity. My boys know that they have to be combed before they go walking.
Hold the hair with one hand to prevent skin and whisker tugging, and use the other hand to comb. Be careful not to catch whiskers in the narrowly set teeth of the comb.
One of the members here with a Grand Champion show Yorkie has written that her boy isn't enthusiastic about having his mustache combed, so take heart.