We have two but had to seperate them because:
1) The male is growing quicker than the female
2) The female had a tail nip when we got her
3) The male was stealing all the food and being really dominant
We will hopefully pair them up when she gets bigger and better! But not have them together all the time.
Also, to convince your Mum, my brother is ten and he has tamed and cares for the two beardies himself. They are quite easy to look after. Our Mum wasn't sure at first but she is totally besotted with the beardies and the iggy! Not too keen on the Royal though!!
NB: We were told that feeding costs for 1 beardie would be about £5 a week, in fact its more like £10 for live food plus your veg too (but we have this anyway) Our male eats a box of locust a day!! For the pair we spend approx £20 a week on live food and veg!!