i need your advise

ok i got a concern here w/ my new puppy Mico , right after my shih tzu Angelo died last Jan 11 , i bought right away a 6month old shih tzu Mico , coz Pipay and Angelo grew up together they get along right away and till i bought another princess type shih it was my dad’s gift for my mom on her bday , it was a lost to me right after Angelo died im not looking for a substi for angelo but just a playmate for Pipay , its almost 3weeks till i got them together but Mico is grumpy towards me and Pipay doesnt like to play w/ him for a reason i think she is looking for her buddy Angelo , but slowly she accepted him but still mico still grumpy to her and me , i picture his behavior as quiet and a loner he likes to play but he leaves me right away , when i take him for a walk he doesnt like walk he just sits on the road even though the time i bought he likes the leash so much , he likes the food , pipay shares w/ him her food but he just snobs her so instead of making pipay happy , she just snobs mico and tries to gaurd Yuemi and Chewy (angelo’s little bro 2nd batch of Dam Dam and Violet’s Litter)  she plays w/them and eats w/them rather than w/ Mico , if Mico wont be happy in our house i wont insist myself to him , i am concern coz i want him to be happy  but he keeps to have a fight w/ pipay , should i return him back to the pet shop i bought him or trade in him w/ other younger puppy or sell him? im giving him lots of time to be w/ me but he seemed to be far away .. i would love to hear from your advices till then .. be safe .