Curio, breastfed babies shouldn't be weighed more than once a fortnight to account for the up and down growth of breastfeeding. You are doing great, keep going!! If they're happy, lots of wees, and a soft, mustard coloured poo every few days, that's what they should be looking for!! Much more accurate than weighing every week!
Babies aren't supposed to jump up through the centiles!! You take from what they weighed 2 weeks in, (after the initial weight-loss after birth) and then hope they stick to roughly that centile throughout the growth. Jumping up the centiles means you're over feeding them (unless they are small babies to very tall parents etc IYKWIM!!)
Have you downloaded the breastfed babies charts from WHO website? They're supposed to have updated the red books with these, but it seems to be a bit slow getting through! The older red books are based on American bottle-fed babies, and we all know the obesity problems over there!! Anyway, follow this link and then plot the weights and hopefully they'll look more favourable! Take them to your next weigh-in! www.who.int/childgrowth/standards/height_for_age/en/index.html
Also, breastfeeding definitely doesn't inhibit speech!
As for not letting them weigh them, my friend exclusively breastfed triplets and resorted to hiding behind the sofa as the HV wanted to weigh them so often and was trying to force her to top-up. She just didn't believe it was possible to breastfeed triplets! They are now perfectly healthy sized 4 yr olds, and were breastfed until they were well past 2 yrs old!! They're taller than my 2 despite being younger! It's a sad state of affairs!