First I should establish that I have over forty years experience and knowledge in the use of lime mortar.
You state that your house dates from the 1900, therefore the binding would be lime mortar and it is essential that any repointing must be lime mortar and definitely NOT cement mortar. Firstly they are not compatible, no adhesion occurs between the two.
Rake out joints to a depth of at least 12mm and thoroughly brush clean
Spray dampen joints and repoint using 3-1sharp sand/NHL 3.5 lime, mortar
Strike off excess mortar, compact with bed jointer and finish with tapping the mortar with the stiff stipples of a churn brush, leaving a flush finish with an open texture. This aids moisture evaporation and is aesthetically pleasing. This is how the brickwork would have been finished when the house was built.
Do not even think or be persuaded differently.