To what limit does raising a merc in the company of another class affect its inherent disposition? Taking into account the natural differences in personality between each individual merc of course. If raised from birth in the presence of Scouts, will a Sniper grow to be loud and affectionate in the same way? If taken in by Spies, will an Engineer develop more of an affinity for destroying advanced tech than building it? Could a Medic theoretically be brought up like a Soldier? So many questions.
I have been running studies on this myself due to my own curiosities on the subject. Homo Manncois being so similar to Homo Sapiens, it is easy to assume they can be just as adaptable as humans, who overall have almost no instinct and are primarily nurture based. However, anyone who has studied mercenaries even briefly can see that they have extremely strong instincts that guide them into maintaining nearly identical behaviours with others of their class.
Of course, there is variety. They are not just identical clones of each other, despite all their similarities, and subclasses show that mixing classes can result in behavioural and instinctual changes sometimes, since not all cross class relationships result in a subclass. So, an Engineer and Soldier pairing won't always result in a Battle Engineer, sometimes it will result in a perfectly normal Engineer or Soldier (or a different class, and other pairings can result in Battle Engineers).
Of course, the fact that the classes do have variations means that there is some influence from the nature they are raised in. A good starting point I began with was observing how Snipers, who largely live on their own, still behave almost the same even when they are not raised together and are in fact from wildly different backgrounds. That makes it clear that the instincts every Sniper class mercenary has are strong enough to cause them to tend towards the same behaviours.
However, I also noticed that Snipers who are raised in nests (typically of Snipers) instead of by other class parents that they often leave when young can cause Snipers to be more willing to stay in packs of other Snipers, and ultimately be more willing to work together with same colour packs. So that made it clear that I had to research further to see how much nurture affected the mercenaries, beyond just Snipers, and caused variations in behaviour.
To get it out of the way, every class and subclass have very strong natural instincts and genetic traits that cause them to maintain certain personality factors even amoung their own variations between each other. So while a Sniper raised with Scouts may prefer Bonk! to pure black coffee and be more accustomed to and comfortable with physical touch and the loud noise they make, the Sniper will never be loud and affectionate to the degree Scouts are, or even close. But they will be louder and more physically affectionate than Snipers raised alone or with other Snipers.
Similarly, while an Engineer could never be raised to hate machines or want to destroy them, they can be raised to be more secretive, willing to lie, quiet, and less affectionate. An Engineer raised with Spies could even go so far as to prefer more expensive cuisine to the typical Southern US style fried and comfort food affair, and/or to prefer wine over beer, but the base instincts of liking machines and keeping them safe is far too strong for any method of nurturing to change it.
Medics raised by Soldier can adapt more traits similar to Battle Medics, but they never go so far as to be able to be mistaken as Battle Medics. Overall, just like less sapient animals, mercenaries have extremely strong natural instincts that tend them towards specific behaviours dependent on class or subclass. But despite what some of my coworkers believe, mercenaries are fully sapient.
So yes, raising a mercenary surrounded by other mercenaries of a different class will cause the odd one out to behave more like the majourity mercenary; however, the limit is pretty low. It affects disposition to a degree and food and drink choices - it also affects clothing choices, so a Sniper raised by Scouts for example would tend towards outfits that appear like a mix between a Sniper and Scout's - but their base instincts that make them what class they are are extremely strong and can't be influenced even by being raised like an "opposite" class to themselves.
I am still studying how much nurture can affect a mercenary into becoming more similar to a subclass; as I said, Medics raised by Soldiers are similar to Battle Medics, but Battle Medics are genetically different and thus they actually have Soldier-like instincts while regular Medics do not. It's become clear that Medics raised by Soldiers get along better with true Battle Medics than Medics raised by Medics, but they differentiate between each other and I can differentiate between them.
I hope that answers your question adequately. I may be the Sniper expert at MPNR, but I have good knowledge of all classes due to my being the person who captures and designs the habitat for all the mercenaries here. I've studied all of them extensively and continue to do so.