I'm feeling that, more important than future prospects, is the question of how the practicalities are lying, in a few months time, when the opportunity to travel actually presents.
Most of us, I'd wager, or those of the age to have young kids, have sex/have romance/ have partners, so if Dad has a relationship now and it were to continue, and his partner were to move moved in, by the time of this trip, it may be another factor to weigh in - whether she'd like to move in to OP house for the 3.5 month period, also .
If Cupid arranges it for Dad to experience shorter- term relationships, and he is wont to be both dining out and having sex, whilst OP is doing the parenting - he'll have to work in some day-time romance, that's if he doesn't work full-time, or some childcare, to give him a chance to keep his new romance going . So again, from this point of view, and the 'his getting jaded' point of view, it's all about the practicalities, of whether his parents, if he has them, or OP's parents, can help out, move in, pick some entertaining duties.
If he lives with an older child whom he had before the girls came along, that is another factor to weigh in. Factoring in is important, and also building into the planning some kind of flexibility and wiggle room, in case unexpected events occur, during the 3.5 months. If OP needed to abandon study experience because of one of these potential unforeseen events, would it reflect badly on her? If yes, then don't do the trip,, I'd say, as you need to factor in the ability to change your mind and come home early. Ultimately, there must always be the capacity to put the children first in the unlikely event of that 'things going wrong', unlikely but not to discounted outcome.
If this is a ex- couple scenario, in which OP and children's father had once lived together, but now, do not, then any changes to living arrangements and relationship status, would have happened, most likely, within the last four years ( the lifetime of the youngest), even less - two years maybe I'd be thinking it might be work asking a child expert about the impact of another quite big change in the lives of the girls. Maybe , this isn't an ex-partners context, but a co-parenting context which hasn't ever involved the living together experience. I'd think a context in which Dad has been the less committed in his career, and the more hands- on of the two parents, would make the stay abroad most smooth, especially if family members around to help with child entertaining. But, I'd say, don't frame all this as a women's equality issue, but instead frame it as a project which needs a lot of strategic planning.