Answer: Miniature roses vary in their sizes; micro-mini roses can remain under 12" high, mini roses can grow 24-36" high and semi-mini roses can grow even larger. I think for now your roses will be happy in the same container but you will probably want to separate them after a year or two. Roses need good air circulation all around to help avoid diseases. If they are crowded and competing for sunshine, nutrients and water, they may be more prone to disease.
Miniature roses have the same growing requirements as standard sized roses; lots of sunshine, deep watering during the spring and summer months and regular feeding to keep them blooming. Because yours are in a container, I'd feed them with a half-strength dilution of liquid fertilizer (Miracle-Gro, Peter's, etc.) every 2-3 weeks during the growing season rather than risking root burn with less frequent, more intense fertilizer applications. Be sure to remove spent blooms to encourage lots more flowers over the summer months.
Enjoy your roses!
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