You don't have to let them breed first. They should only have to be kept in long enough to get them trap trained and trained to a feed call. Although being new birds, personally I would want them to breed first just in case the new ones got lost or killed. I'd want to get some of their blood in the flock first.
Yeah if you want them for breeding it let them start breeding. Otherwise, the birds only need 2 weeks or so really. Just feeding them once a day in the evenings for 20 mins with a feed call. Then let them out hungry in the evening for acouple hours and call them back in. Its best to have a trap door so you can trap train them but i dont, and a lot of other people i know dont. They may or may not pick it up. Sometimes they can be dumb. My loft is all open so they can see inside from the sides and confuse them but if your in a colder climate they may do it easier. When you have a flock of atleast 10 birds which fly around. you could add 30 birds keep them for 5 days and they wouldn't leave most likely. Last time i went out of town, my mom had accidentally let out all of my tumblers i took in around only 7 days ago. She said they just flew with my tipplers and came down at night. Those birds had food in full time and no trap training or feed training. I took there food at yesterday morning and let them all out and they came all back down yesterday, most trapped in with my tipplers but a few went in the right loft. No birds left. Long story but its to show that these birds really dont fly off often. Only birds you have to worry about are homers. My fellow down my street had birds get out the day after or the night getting them and just perched on his roof. If a bird doesn't trap in your loft its most likely on the roof or nearby, wait till its pitch dark and grab it.
sorry to hear that. I think keeping them in longer than a month is really not needed and possibly hurtful. Next time place them in a cage they can see out of and set them outside the loft for awhile for acouple days.
i kept them in cage's .. the first time when i flew them they came back but next day,when i opened the cage no one of them flew the just roamed on the floor and getting back to cage after sometime one pair flew and all them flew away following the first pair ...