I flew with Qatar a few years ago and the standard Economy baggage allowance was 23kg per person. So the three of you should be OK with a combined weight of 69kg. TBH, if you are planning on taking any more than that, it will be a serious amount of luggage to carry.
Does your E-ticket or any of your paperwork say what your allowance is? Usually it is mentioned somewhere on the paperwork.
Just a word of warning, my case weighed in at 25kg and the Qatar check in attendant at Heathrow made me take 2kg out of my case and put it in my hand baggage.
