Not unexpected - some of the evening flights are operated by SQ so MH availability is limited and Dec is a busy travel period of course.

MH is by weight, not piece, so two is OK for any passenger. If you travel economy on this sector you'd get 30kg+20kg = 50kg max 2 pcs each.

I haven't done it KL but both times I've needed my oneworld allowance at Heathrow they haven't been familiar, haven't been able to check with anyone and in the end have just gone ahead to get rid of me!