changing rabbits from muesli

i have two mini lops age 18 months, i have had them since they were 12 weeks and continued the food that they came to me eating which is a muesli mix, i have tried them on 5 different types of pellets and they just won't go for them. i currently mix in about 1/2 of oxbow pellets which i think are just getting thrown out rather than eaten. i've had bunnies 22 years but these two just won' comply. what pellets do your rabbits eat?
tried excel junior when they were little, select, woodlands from pets at home and Chudley’s mixed in with the rabbit royal (yuck)

It may be the quantity which is making them "fussy". How much do they get every day? It is recommended that you should do a change-over over a 10 day period, adding more pellets and less Muesli each day.

when i first got them echo was seriously underweight (400g at 12 weeks)as his sister was eating everything, i think i have had a bit of fear if i cut them off he's going to starve again. So we were allowing too much food we're reducing the muesli now and allowing less with lots and lots of hay, will be introducing indoor pellets or Harrington this week