Share the brush
Cats have very strong senses of smell, and they use scents to communicate with each other. When cats are bonded they will create a “group scent,” an act you’re witnessing if you see your cats rubbing up against each other. In fact, you’re being included in this group scent when your cat headbutts you.
Sharing scents helps your cats become familiar with each other, and therefore comfortable around each other. You can help this process along by using the same brush to groom them. Before brushing, let each of them sniff the brush. Only use the brush to groom your cat if she has no adverse reaction to smelling your other cat’s scent on the brush. If she pulls away, hisses, or growls, respect her feelings and don’t force it.
Forcing a shared scent can cause even more stress and territorial issues. Instead, keep trying each day, only brushing the second cat once the reaction is positive or neutral.
https://iheartcats.com/5-ways-to-help-your-cats-bond-with-each-other
Whether dogs, cats, or a combination, I’ve used the same towel, gloves, or brush, to pet them and create a group scent. It has always worked for me.
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