#Python 3.6 - 286 241 224 bytes

def x(L):X,Y=L.split();E,D=' '*11,'_'*12;print(f"""{' '*18}{D} 
(\   ___   /)    /{E} \\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({E})  <     {Y}
 (  ‘> <’  )    \{E}   /
    /    \       \{D}/
   /      \ 
  ‘ – “ - ‘""")

Input:
x("Silent Night")

Output:    
                  ____________
(\   ___   /)    /            \
( \ (‘o‘) / )   /    Silent    \
(           )  <     Night
 (  ‘> <’  )    \              /
    /    \       \____________/
   /      \ 
  ‘ – “ - ‘

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.

Python 3.6 - 286 241 224 bytes

def x(L):X,Y=L.split();E,D=' '*11,'_'*12;print(f"""{' '*18}{D} 
(\   ___   /)    /{E} \\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({E})  <     {Y}
 (  ‘> <’  )    \{E}   /
    /    \       \{D}/
   /      \ 
  ‘ – “ - ‘""")

Input:
x("Silent Night")

Output:    
                  ____________
(\   ___   /)    /            \
( \ (‘o‘) / )   /    Silent    \
(           )  <     Night
 (  ‘> <’  )    \              /
    /    \       \____________/
   /      \ 
  ‘ – “ - ‘

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.

#Python 3.6 - 286 224 bytes

lambda X,Y:f"""{' '*18}{'_'*12}
(\   ___   /)    /{' '*12}\\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({' '*11})  <     {Y}
 (  ‘> <’  )    \{' '*14}/
    /    \       \{'_'*12}/
   /      \ 
  ‘ – “ - ‘"""

Output:

Resulting string when 'Silent','Night' is passed to the function :
                  ____________
(\   ___   /)    /            \
( \ (‘o‘) / )   /    Silent    \
(           )  <     Night
 (  ‘> <’  )    \              /
    /    \       \____________/
   /      \ 
  ‘ – “ - ‘

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.

#Python 3.6 - 286 241 224 bytes

def x(L):X,Y=L.split();E,D=' '*11,'_'*12;print(f"""{' '*18}{D} 
(\   ___   /)    /{E} \\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({E})  <     {Y}
 (  ‘> <’  )    \{E}   /
    /    \       \{D}/
   /      \ 
  ‘ – “ - ‘""")

Input:
x("Silent Night")

Output:    
                  ____________
(\   ___   /)    /            \
( \ (‘o‘) / )   /    Silent    \
(           )  <     Night
 (  ‘> <’  )    \              /
    /    \       \____________/
   /      \ 
  ‘ – “ - ‘

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.

#Python 3.6 - 286 224 bytes

lambda X,Y:f"""{' '*18}{'_'*12}
(\   ___   /)    /{' '*12}\\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({' '*11})  <     {Y}
 (  ‘> <’  )    \{' '*14}/
    /    \       \{'_'*12}/
   /      \ 
  ‘ – “ - ‘"""

Input : s('Mother','Mary')

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.

#Python 3.6 - 286 224 bytes

lambda X,Y:f"""{' '*18}{'_'*12}
(\   ___   /)    /{' '*12}\\
( \ (‘o‘) / )   /    {X+' '*(10-len(X))}\\
({' '*11})  <     {Y}
 (  ‘> <’  )    \{' '*14}/
    /    \       \{'_'*12}/
   /      \ 
  ‘ – “ - ‘"""

Output:

Resulting string when 'Silent','Night' is passed to the function :
                  ____________
(\   ___   /)    /            \
( \ (‘o‘) / )   /    Silent    \
(           )  <     Night
 (  ‘> <’  )    \              /
    /    \       \____________/
   /      \ 
  ‘ – “ - ‘

Note - The version is 3.6 where string literal formatting was introduced. Hence, this won't work in earlier versions.