Start with how they behave at the closed door
Before any face-to-face meeting, the closed door between the two cats tells you most of what you need to know. A cat who is nearly ready eats her meals near that door without hesitation, sniffs underneath with a relaxed body, and then wanders off to groom or play. Curiosity looks soft: ears forward, tail up or neutral, maybe a roll or a rub against the door frame where the other cat's scent is strongest. A cat who is not ready crouches at the door for long stretches, growls or yowls at sounds from the other side, lashes her tail while staring at the gap, or refuses food placed anywhere near it. Those behaviours are information, not stubbornness, and pushing ahead against them usually buys one frightening first meeting that sets the introduction back far more than a few extra patient days would have.
Scent and sight stages should already feel boring
By meeting day, the earlier stages should have become uneventful. Scent swaps, where each cat sleeps on bedding the other has used, should provoke a sniff and little more. Feeding on opposite sides of the door should be a routine both cats treat as normal. If you have used a screen, gate, or cracked door for visual contact, both cats should be able to look, eat a treat, and turn away by choice. Boredom is the milestone you are waiting for: when the other cat's smell and sight no longer organise either cat's whole day, direct contact is far less likely to tip into a chase or a stare-down. If one cat still fixates, split the difference and progress only the calmer stages for the reactive cat rather than restarting everything for both.
Run the first meetings like short, fed rehearsals
Choose a room with escape routes and hiding places, bring both cats in at a distance, and feed something each of them loves so the first shared minutes are paired with food rather than confrontation. Let them choose how close to come. Curious approaches with loose bodies, sniffing, and then disengaging are exactly what you want; a hard stare, advancing crouch, or growling means end the session calmly before it escalates, using a barrier rather than your hands to separate them. Keep early meetings brief and finish while things are still going well, then repeat daily, letting the calm sessions gradually lengthen. Most pairs need several relaxed rehearsals before unsupervised time together is sensible, and a single bad moment matters less if you return to the previous stage without treating it as failure.
Keep the whole household working the same stages
Introductions unravel when one person follows the stages and another decides the cats should just sort it out and opens every door. Agree the current stage, the signals that move the pair forward, and the signals that send you back a step, and make sure children and visitors know not to carry a cat into the other's space for a surprise meeting. After the first successful meetings, protect the peace with doubled resources: feeding stations apart, litter trays in more than one area, and resting spots neither cat has to contest. If weeks pass with no softening at the door, or either cat stops eating or starts hiding through the day, ask your veterinarian for guidance, since pain, anxiety, and a difficult past can all stall an introduction. Inside KinsLe, Family Sharing puts this pair's introduction stage, door-side observations, and feeding spots in front of every family member, so nobody advances the plan by accident.