Saffron-is their anyone you know and trust to build a couple of catruns in the garden-safe environment and gives them freedom or if not it would be well worth spending a little on one/two-great investment and priceless for the peace of mind you as a slave will get
Know it's a pain and can be costly but catflaps imo not good to have around pedigree's-Siamese/Ori's(not sure on Burmese
) are very cunning and clever and will sus any means of escape especially when in call,very nosy too
Also though your moggies are healthy-they may bring diseases/virus's back in with them putting your new cats/kittens at risk
Your moggies will quickly adapt and be just as happy-i promise