Just go on as if they hadn’t come around. Normal level family ‘noise’ during the 7am-10pm day. Chalk their visit up as though from people without in-tact mental faculties (which is what practically everyone is at newborn stage, PFB). It’s possible they had no idea that it was 6pm, or a Saturday 
If/when they come around again with a noise complaint, you’ll no doubt be better prepared with a gentle-but-firm, assertive response. This situation calls for what’s known as the ‘sh*t sandwich’ approach, I think.
‘Debbie, we feel for you. These last 8 weeks have certainly reminded us of those crazy sleep-deprived newborn days with our two. It is hard when they’re crying all the time, hard on everyone.
Thing is, we need to get on with our family life, too. We’ve got intense home-schooling going on xx hours a day, and limited play options for two wriggly kids the rest of the time. DH & I are working xx hours a day from home. Sometimes, you’ll no-doubt hear our family life through the walls too. Music, squealing board games, tv, zoom meetings and probably some squabbling too! We’ll try and keep the noise coming through the walls from our side to a dull roar after xx and before xx time, as always.
Now, if we can pick up a few bits for you or take in a delivery while you catch up on sleep feel free to ask. Remember that crying babies and Covid lockdown won’t last forever- we’ll all survive I’m sure. Good luck for tonight, we’re all ‘fingers crossed’ over here!’
Or something like that. Make your point, and outline your needs clearly. With a smiley, sympathetic tone. Then email it to them, cos their retention of your information will likely be near zero!