OOF. Two beagles would be rough, they're going to feed off of each other's vocalizations. Lots of good suggestions here - I have a couple of new ones for you:
Set up the kennels in an area of the apartment with the least neighbour interaction. Perhaps they have a corner unit and one of the rooms has no neighbour? Or choose the kitchen or living room because rooms are usually back to back or stacked over each other in an apartment layout, and the noise transfer would be more disruptive in the bedroom areas versus the kitchen/livingroom/bathroom.
Try one of those pet cams with two-way sound. They'd get a notification when the dogs make noise, they can get on the app, and distract them by speaking to them. Some models even come with the option to launch treats (may or may not work with a kennel).
Try to soundproof the area as much as possible. You can buy sound-deadening foam for podcasting/music recording etc... on
Amazon for example. Both for neighbours and to keep the dogs from being triggered by noise. Add fans/white noise etc...
Don't just put them in the kennel when leaving for the day. Put them in for short periods in the evening as well, and on weekends so you can actively correct them when they make noise, then let them out when they're calm/quiet. This is a crucial part of crate training that works best done right from day one, but can still work to improve barking later as well.
Befriend one of the neighbours, introduce yourself and explain that you're working on correcting the behaviour. When we were kennel training in a townhouse, we did just that, and they were very receptive as a result. Sometimes a person just wants to know that their neighbour isn't an uncaring jerk, and that goodwill goes a long way.