Ok striking (kicking with front legs) is NOT ON!!! That and rearing make me shudder, striking is more often than not out of pure aggression and your horse dominating you. He needs to be gelded as soon as his testicles drop and sent off to someone who has extensive experience in handling pushy colts for a while. If they get away with this behaviour at a young age, it will be one hell of a job trying to get it out of him when it comes time to handle him once he's fully grown. Why a first time horse owner has purchased a young colt and a pregnant mare eludes me, but it's too late now so cure will have to be the way.
As for separating them... how is the mare when you take the colt away? If she is very attached to him and will panic when he leaves, you'll need to find her a friend, just a cheap shetland or mini, or a friends horse that is happy to live with your mare for a few months. If you separate them and your mare panics, she can very easily abort the foal. But equally as dangerous is having her in with a colt, even at 7 months old, he may cause he to come into season and slip her foal.
If the mare is ok about having the colt taken from her sight, get him out of there and to a trainer, or into a paddock full of horses that will boss him around and put him back in his box would be more appropriate for a young horse. it would certainly be best for your mare to have a friend still though, it's not fair to keep any horse, particularly a pregnant mare, in isolation.