Wouldn’t bother getting bigger mam bottles before they’re born just in case they don’t like them.
Sounds like your have plenty, I’m planning on getting 9 this time round, I had 6 each time in the past and a few more would of made my life easier!
with my little one we got one of those MAM bundles that had 2 small bottles and 2 bigger ones, so we used that and then bought 2 more little ones. we kept the bottles but changed the teats when needed and then when she was about 6 months and less likely to get colic we swapped to the MAM sports bottles and had about 4 of these
I think that would be plenty we used 6 mam bottles first time around