I have found having multiple Siamese is fine if they have shared bonds. As a single person I had two Siamese cats, different ages, and they became real companions only after several years. The older one, who was bored, which is why I got the second, was jealous of the younger one. The next time I got two kittens at the same time, which worked excellently. We have done that since then, and whether we have had two, three of four cats, it has worked for us to add kittens in pairs. Otherwise a kitten tends to make an older cat fed up, kittens are so rambunctious. When we have two kittens, they play with each other and spend down time with the older cat, which is what the older cat likes. Once the kittens have grown up, they have become companions with the older cat, not just tolerated. I think our cats are extra well bonded, too, because they sleep in their own room at night (my husband, cat lover that he is, can't sleep well if cats are on the bed). I think, over time, sharing the same bedroom leads them to learn to sleep together, making them that more companionable at any time of the day.