Excellent questions.
Let's figure out what the answers could be...
I'll take a couple of guesses...
First possibility - you have three minion seeds and you want to grow them for the friends who helped you. Easy peasy - plant them one at at time - in any soil and they'll grow to be minions in about a week. Harvest - give away - tada.
First and a half possibility - you have three minion seeds that you want to grow for friends - and you want to try to crossbreed them hoping for seeds for more minions. You'd need to plant the seeds in thanalan grade 3 soil (90% chance of crossbreeding) - and plant them in an order that the crossbreed based on experiments other folks have done. From the lodestone forum - the crossbreedings for minions that have been found so far are (note - these may or may not be completely correct):
Onion Prince:
- Krakka + Azeyma Rose
- Krakka + Mandrake. - alt. Mimett Gourd
King Tomato:
- Krakka + Broom-bush
- Krakka + Jute
- Mimett Gourd + Almond
Eggplant Knight:
- Krakka + Star Anise
- onion prince. + Krakka
- Wild Onion + Onion Prince
Garlic Jester:
- Mandrake - Garlic Clove
- random result - Flax(harvested) + chamomile.
- Dzealma Tomato + Mandrake
Mandy Queen:
- Nymeia Lily + Mandrakes
These are what I've seen on that forum - they have not all been confirmed as happened more than once and for different people... But they are what had been posted so far (I've been trying to follow the discussion thread and keep updating the list of cross breeding results).
If you happen to have a minion seed that can be crossbreed according to these possibilities - then give it a shot and hope for the best. How do it work? I think that you would plant Wild Onion and then Onion Prince right next to the wild onion (used grade 3 thanalan soil for the onion prince) and grow grow grow and hope that the harvest of the onion prince results in and eggplant knight. I may have the planting order backwards - so search around to find the combination and get the order correct.
Second possibility - you have a minion seed and want to grow more of them - similar to the above - but hope to plant one seed and crossbreed it with another to get another minion - and eventually grow the minions... Sort of both of the above - but longer. Many minions can be grown from seeds you can gather - so so that if you have the chance.
When growing minions - I suspect that the soil types that won't do much are the HQ flavor (as I don't know of any HQ minion) and the higher yield soil probably won't do much either as you will likely only ever get one minion from a seed. This translates into try the thanalan grade 3 soil for cross breeding and setup the seeds in the 'right' order and hope for a cross breeding to get another seed for later.
Good luck!