I believe it is best to approach problems step by step and work through them logically.
This requires having as much information as possible in order to offer the best possible advice or suggestions.
One must always realize that birds are not going to do what you "want" them to do. It is always best to be prepared to deal with any eventuality when it comes to housing.
Just like people, some budgies get along well with one another and others do not.
I have four separate F040 flight cages.
For awhile, two of my budgies could be together during the day but never at night. Come evening, one of them would not let the other perch -- anywhere!
Allowing them to each have his own cage solved the problem.
Over time they finally reached the point where they could even be in the same cage at night but it took several months.
So, what you are experiencing now with Mylo and Merri is just that. It is what is happening "Now". That doesn't mean it will "always" be this way and there may be options we haven't yet considered that are entering into the equation.
Let me ask you this --
How much time per day are your birds out of the cage?
You indicate Merri isn't allowing Mylo to eat -- are we talking about seed only or does this include pellets and vegetables as well?
Do you keep pellets in the cages 24/7 and provide their seed rations morning and evening in "foraging" situations?
I have four budgies living together. Occasionally they squabble over food or toys.
Whenever I have seen one of them seem to cause trouble with another, I watch them closely to figure out what in the cage needs to change that may lesson the squabble.
At times I have had to move perches to the same level when they were often trying to all squeeze on the same perch. At times I have had to move perches to different levels, so they are not always seeing each other. I have had to buy extra swings, because I have 4 budgies and I had only 2 swings. They squabbled over the swings, and buying extra actually solved the issue.
I have dealt with a budgie not allowing another budgie to eat in peace. I rearranged the cage, bought a couple more food dishes, and placed the food dishes all around the cage at different levels. They now always are able to eat in peace. I have many perches that have the food near it, so all they have to do is turn to eat. They don't even notice who is eating or not.
I do rearrange toys weekly and occasionally rearrange the whole cage. I believe doing this helps keep them from being so bored and helps them live in peace.