I got a crate when I got the 3 moggie kittens but in the end I didn't use it. I came to the conclusion there were enough places in the house for them to find their own "safe" area and I didn't really want to keep them confined in such a small space. I did keep them shut in one room for the first few days while I was at work and I made sure it wasn't a room that Dolly (my Bengal) regarded as hers. I had some scary moments, including Dolly disappearing for 3 days, but things have now settled down and she tolerates the kittens, even playing with them now and again.
If you can get pieces of bedding that they've both used, then you can try swapping those over so that they get used to each other's smells. Active play and treats are also a good way of getting them to share space.
Overall though, the key advice I'd give is to be patient. There may be times when you'll worry that you've made a huge mistake but you have to take things one step at a time. I always think back to wise advice I was given once that you can only eat an elephant in bite size chunks - it's true of so many situations in life