Randomally introducing Cats?

[JeanieBeanie]

My future husband(who I will just call my husband) and I are living with his father until we've saved up for a house. The three of us purchased a Himalayan cat together, named Meela, who is 8 months old. My husband's mother lives over a couple hours away and just purchased two ragdoll/himalayan kittens who, I think, are only a few months old; she comes to visit us about once or twice a month.

Since she got these kittens, she wants to bring them to the house with her. They've been introduced this weekend but it didn't go overly well. Meela seemed to be getting used to them but when they started to 'play' she'd swat at them, or pounce on them, with her claws out while hissing and spitting.

My husbands Father, and his Mother, want Meela to get used to this, while I think that it's not good for Meela for them to be coming in and out of her territory at random. The most that these kittens would be staying here would be 2 days at a time, and maybe for a whole week during Christmas.

What do you think? And if Meela can get used to this, what is the best way to approach it?