In my personal opinion, if they are happy indoors then there is no need at all to let them out. The fact that you are concerned already shows me that you wouldn't really be happy about it anyway

As long as they have each other and plenty of toys and attention, they will not miss out at all. If you start letting them out and then something happens or you decide you want to keep them back indoors, it will be much harder for them xx

Hope this helps

Lou
xx