Hard and fast rules are not helpful as they don't take account of need! Some kids need the closeness that co-sleeping provides,others are perfectly content in their own cots/beds. My DGS does not co-sleep and never has..but his mum , my DD1 did! My DGD1 did co-sleep sometimes but now 6 she does not (unless unwell) need to. DGD2 still sometimes co-sleeps at 3 but it is reducing! her mum, my DD2, was always in our bed..and either me or her dad went to hers! We are all happy and healthy and enjoy being around each other..so no harm done!
Parents-in-Law. What do/did you call them?