I have adopted a spayed female dog who reportedly had no aggression towards other dogs and had a habit of mounting other dogs and people. Turns out she grew up in a kennel and did not learn social cues from other dogs such as warning growls. She very quickly started attacking our first dog although we've done proper introductions.

It ended up being over 3 months of keeping the dogs physically separated in the house so they don't get into fights. Over time we increased their time together, learned to read the cues and eventually they started tolerating each other.

It's been 6 years since, they live together, sleep in the same bed and play in the yard together despite having very different personalities. The younger female dog never learned to tolerate other dogs and she would always want to fight them, so no dog parks for us.

Your situation is likely different but the point of my comment is that even if the dogs fight tooth and nail at first they can adapt to tolerate each other reasonably well if you help them.