Hi! This thread looks friendly and productive, so I'll bite :)
Here are 4 core judeo-christian ideas that I find helpful on this topic:

1. Transcendent morality. If morality is to be resilient, it must transcend culture, preference, etc., otherwise it can be changed or over-turned as convenient.
If morality is purely relative, a matter of agreement, then the concept of an inalienable right is not meaningful.
Philosophy has tried to find a different ground for morality, as the parents mentioned -- but that has not been successful, and I don't think that it can be.

The judeo-christian perspective here is of course that moral standards come from God, thus they are absolute and transcend our opinions. More specifically, they are not "law" per se, but something deeper: They reflect God's character, which _defines_ morality. I.e., God _is_ morality.
For instance, Love and Justice are core moral standards because God is Loving and Just, or more precisely, we learn what Love and Justice are by looking at God.

2. The _Imago Dei_. This is the idea that makes transcendent morality applicable to humans. Morality needs to be universally applicable in order to be sustainable, otherwise it's trivial to enact restrictions -- e.g., that it need not apply to the rulers, to Jews, to Republicans or Democrats, to Muslim minorities in China...
The Imago Dei is the notion that humans are created in God's image, and therefore have inalienable dignity _deriving from his_.
This notion is different from more utilitarian ideas that we have worth and dignity based on e.g. our intelligence, ability or so on, and is a prime defense against all kinds of "lebensunwertes Leben" (being the nazi phrase) ideas.
Incidentally, this is also why Christians are so opposed to abortion and have been since forever (roman times and even Old Testament times): The idea that the worth of the baby is not dependent on their awareness, ability or whatever (which many disabled or ill people also do not have), but on on their humanity as such.

Historically, anything from due process to property rights has been argued from this: Much of it in Old Testament times, e.g. but by far not limited to the well-known 10 commandments, then much more in New Testament times, which was then expanded upon by the early church fathers and christian-influenced philosophy. The abolition of slavery and much enlightening thinking might well not have emerged in a different context.

3. Universal Sin. The concept that all human beings are fallen and in need of redemption is what makes morality and safeguards necessary in practice. This is the knowledge that there is no _inherent_ difference between e.g. nazis and me -- I am equally capable of such atrocities if left to myself. Therefore, ordered liberty is required - government, law, and institutions to guide and restrain us.
The acknowledgment of Universal Sin promotes compassion, because no-one is intrinsically worse than me: This strengthens the practical value of the Imago Dei and weakens us-versus-them ideologies like nazism or intersectionality.
It also both requires and limits government, since an effective form of government needs to take the sin of the government into account as well as that of the population.
This is where separate branches of government, checks and balances, (mostly electoral) accountability and related ideas were derived from.

4. _Subsidiarity_. This is the concept that the smaller and closer the unit or relationship is, the more crucial and stable it is. This ties in to 3., because the effects of sin compound with larger and more abstract units. Sin also has much more pull if given more room - see Lord Acton's famous quote about power and corruption :)
I.e., it's much easier to be compassionate and efficient towards a wife or neighbor than towards "Comrade nr 25556 of the district of Eurasia".
This idea has led to a strong emphasis on the family, neighborhood and local church as core institutions where the primary "government" is better placed, as opposed to a large and anonymous bureaucracy.
This is were representation, federalism, small government and related ideas come from, and incidentally, why I find the US Constitution as intended far superior than the direction American politics has taken in the last 100 years (big government, bureaucracy, centralization, homogenization).

I hope this helps you understand me a bit, I'm looking forward to continue this conversation! :)