An old (17th c.) proverb holds:
A swarm in May is worth a load of hay; a swarm in June is worth a silver spoon; but a swarm in July is not worth a fly.
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And for the very reason you mention; they won't have time to build up enough food stores to survive the Winter. Most likely you'll have to combine them this Fall.

You can do it. Michael Palmer runs 7-800 colonies and starts hundreds of nucs for overwintering. He runs double nucs in a full hive body and overwinters on top of full size colonies. I don't think he'll mind my posting the following quotes he made when answering similar questions on starting nucs.

"For the first time, I would make up your nucs in mid-July. If you make them too early, and have a strong flow in late July/early August...from something like Loosetrife...they'll swarm unless you do some serious management like removing brood and replacing with empty comb or foundation. If you make them too late, they won't be able to establish a good enough broodnest and will be weak in the spring...at best.
Keeping them small conserves equipment. You start them with only a minimum of bee resources...1 frame of brood, 1 frame of honey, one frame of something...a little brood, eggs, nectar, pollen, etc...and one empty or foundation. Often, if you are nuking non-productive colonies, everything is there in that hive except the foundation."

"I usually make up about 400 such nucs in July. If I was to increase their size to 10 frame boxes, I'd need more than twice as much equipment. And, since I winter them on top of other colonies, twice as many bottom colonies and twice as many boxes to move in November...and again in April."