These are great questions. The key lies in thinking about the reasons some theologians and the church have used the term "objective superiority" about certain states. While folks sometimes still throw around the idea that some vocations are higher or lower than others I think it is important that we let go of such notions. They are too easily misunderstood as "more or less worthy" and things like that. If there is one thing Vatican II tried to get across and make sure the church expressed in the whole of her life it is the idea that every person is called to holiness and we cannot suggest that some vocations lead to holiness while others do not.
Think of it this way one child is born into a family of wealth and privilege while one is not. Both children are well-loved but the first child is also well-fed, clothed, housed, educated, catechized, and given many privileges the second child simply has insufficient or even no access to. We might well say that the first child has been called into an objectively superior state of life because everything necessary to grow into a healthy, creative, loving, and productive human being is built into their home life. When theologians speak of one vocation being objectively superior to another this is what they are speaking of. One vocation has all the things along with the vision and focus necessary to lead one to genuine holiness while others do not (or at least seem not to).
Note well, that objective superiority does not necessarily imply the subjective superiority of those called to such vocations, nor even that such a vocation is the best context for everyone called to achieve real sanctity. The second child in our example may well thrive in ways the first does not precisely because she will respond to the need to strive for resources or be more attentive to the inklings of grace in a given situation than the first child. While the second child may never be wealthy in all the ways the first child is, she may well grow into a better more loving human being.
This may provide a way of approaching your question about marriage vs religious life. Yes, it is absolutely possible for marriage to be a better means to holiness than consecrated life would allow for. Remember that marriage is a Sacrament and is meant to reveal the way human beings love one another and bring one another to union with God. Consecrated life is not a Sacrament and has never been raised to that dignity. Granted, the married couple must build into their lives all of those things religious life tends to take for granted (so to speak) and that is really difficult when struggling to raise a family, educate them, give them all they need to become whole and holy human beings. There is nothing easy in that and the degree of self-sacrifice and generosity involved is truly heroic --- but it is certainly possible. Families may be poor, but they cannot make vows of poverty because they must raise children and give them all the resources they need to grow and mature. Which is harder to achieve? Which requires the help of the Holy Spirit more to maintain a healthy focus? Each is difficult in its own way and where once I might have said marriage, I now say I really don't think we can say. The term öbjectively superior" does not allow this kind of comparison or competition. It simply calls for gratitude!
Still, in either case, the question facing the persons you described will need to be where do I feel most deeply and truly called? Which of these vocations will allow me to be most fully myself, to love most fully and effectively? I doubt anyone ever determines their true vocation by measuring it in terms of objective superiority, for instance. We measure vocations in terms of the humanity they make possible for ourselves and others and this necessarily means too, the ways and degrees to which they reveal God in our world. (Remember that reveal does not only mean to make known, but also to make real.) When we respond to a vocational call we implicitly do so in a way that is optimal in these terms --- it is the best choice for us as responsible and responsive human beings who are called to wholeness and holiness, just as it is the best choice for those whom we will touch because of this vocation --- and therefore, it is the best choice for glorifying God with our lives. Unless the vocation we discern allows and even empowers this in Christ, it really doesn't matter whether in some other sense it is considered objectively superior or not.
The use of the term higher is more problematic (though it is a logical correlate of calling some vocations higher, the church never uses the term lower of vocations). In general, I think it is a term we ought to drop because it is too misleading to be used fruitfully. It pushes us to compare the incomparable, and measure God's love for or valuing of us vs God's love for and valuing of others. It makes it hard to avoid doing these things and that is disastrous for genuine spiritual life. Still, if people choose to use it, it should probably be used in the sense of objectively superior as we have described it in the example above. My preference is to object to it, to point out that every vocation is a call to holiness and every vocation should be given the infinite esteem it merits as a divine call. ALL vocations are calls to a share in God's own life and union with God. They are each and all shares in the building of God's Kingdom. Every vocation lived well glorifies God and makes God (and so too, eternity) real in space and time. Terms like higher and lower simply make no sense in light of these facts.