Beautiful fish!
are you in contact with the breeder? if they've been raised on beefheart mix, then they are pretty much acting as expected re food behaviour
Get them eating your homemade mix consistently, eg, 5 day at least, they eat any time you offer food - are ravenous about it (angels are food piggies
)
Be careful with BH mix as it fouls the tank quickly, expect to do daily water changes with this type of food, if tank were bare bottom, you could just syphon out any leftover food ~10 min after each meal, in a planted tank this is impossible, so just go with daily 25-35% water changes
If you're good at matching tank vs tap, you can easily do 90% daily water changes with angels (like discus), if your tap is inconsistent etc, then stick with smaller daily water change
Then begin mixing whatever alternate you choose - & choose only one - maybe 10% at first feeding, 20% day 2, 30% day 3 etc ... if they begin to get picky, then go to previous day's food ratio
At this point you can let them be a little hungry, eg only offer 70% at each feeding compared to previous week when you were just getting them settled & well fed
Once they are completely transitioned over to the new food, ie they race across the tank & eat madly - feed only this for a week or two; then begin introducing your next chosen food, same method as above.
In time, they should be willing to eat/try anything offered, regardless of it being a completely new food
Some breeders feed a wide variety of foods to juveniles, this begets a fish that will eat/try pretty much anything once sold on, some breeders feed only 1 or 2 foods & neglect to get their juveniles on "ordinary" pet shop fish food before selling on ... when buying angels (or discus) ask when shop feeds fish & return at that time to observe that fish are feeding well - this omits a lot of what if's about new fish
Angels (& discus) can be incredibly stubborn about foods they will/won't eat, of course at the same time they are stressing which means a lessened immune system which can then lead to disease level parasites/bacteria etc. Angels can be very sensitive to water column medications so it's always better to start treating them with medicated food - wait until they are no longer eating & it can be very disheartening.
Seeing how voracious they are (when eating), it's easier to understand how disturbed they are in order to NOT be eating.
Look at the thickness of their bodies from above, they should have some depth even at fairly small juvenile age, if they are "knife" thin, don't but them (or buy realizing it can take considerable effort to bring them around)
Often just daily water change, some salt (I like to use a marine mix or natural salt rather than NaCl but anything is fine - BUT check any table salt for anti-clumping agents, Kosher usually has none as it's coarser) & increased temperature (up to 90F) can be effective "medication" with angels - if you go to
TAF there will be many many posts on angels not eating
Note that increased temp means considerable decrease in dissolved oxygen levels in water column so you need to be very conscious of optimizing aeration (most air pump/stones are not as effective as optimized filters) & some salt if generally advised as well.
I'm not a fan of Melfix or Pimafix as both can be very distressing to angels (& other fish) - while both may reduce water column bacteria etc, neither has been shown to inhibit actual fish active bacteria ie the types of bacteria which are identified as disease agents in either external or internal fish infecttions