Uy, I totally understand your worry, lalo na may family history kayo ng autism, napakagaling mo na nag-observe ng ganito in detail! Honestly, ang regression in speech at the loss of those skills like peekaboo ay something worth checking with your pediatrician or a speech therapist soon, kasi 16 months na sya at ang language delay combined with the regression is worth professional eyes on, hindi lang mama worry. The good news is he's hitting milestones in other ways, his motor skills are actually ahead, he has eye contact, he's engaging with you guys, at he responds to games, so there's lots of strengths there din! A few of my mum friends nag-consult din ng OT or speech therapist at nung na-assess lang nila properly, nakita nila kung ano talaga ang happening, whether it's just speech delay or something else na kailangan ng specific support. Don't panic, but do schedule that check-up lang para makamit sya ng early intervention programs kung kailangan, the earlier, the better talaga for any developmental concerns.