difference between therefore, furthermore, and in addition (to)

these words always show two ideas 1 + 1 = 2. for example, In addition to these arrangements, extra ambulances will be on duty until midnight. ---- this sentence shows two ideas

in addition (to) --- (үүнээс гадна, үүн дээр) the most common 
furthermore --- (цаашилбал) next most formal (in middle of two words in addition and moreover)
moreover ---(түүнээс дээгүүр, тэрч байтугай) the most formal