They do not know each other. The translations from mangapanda and *********** are different, but neither is perfect. Mangapanda is more of a direct translation, so it is better in that way, but *********** attempts to use vernacular that English speakers can relate too, so they are good in that way.
In respect to Tobirama and Izuna knowing each other, what they said in the original Japanese is as follows.
Madara's father: It seems we were thinking the same thing... Senju Butsuma.
Izuna: And Tobirama (as in, " and Tobirama, I believe it was" or "and Tobirama, huh")
Hashirama's father: So it seems... Uchiha Tajima.
Tobirama: And Izuna. (as in "And you must be Izuna" or "and Izuna, huh")
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Basically, they are saying almost the same thing, but in different ways. I don't think that they are personally acquainted, but are aware of each other through the intel gathered on each other's clan. Also, Madara's father seems to be using a mockingly polite tone when he speaks. He may have a personality mixed between Madara's adult one, and perhaps Orochimaru.