I've had that happen to me two. One of my Ruelrs had six sons, and each one of them, married, with little children, asked to join a Holy Order.
First, if I say no-and if they have little kids, I *WILL* say no-that's 100 piety for every "No". But after I say no, they behave live the kids from the Simpsons...
"Arewethereyetarewethereyetarewethereyet..."
Six sons constantly pestering you to let them join a holy order will drain *ALL* of your piety in less than a year...
That's actually like it, yes.
Land them. They shut up if you land them. Stick them as the baron of some place you don't care about and forget about them.
If you're under gavelkind, stick them in a bishropic to permanently shut them up. Or just say "yes" and let them bugger off. It's not like they just stick the kids in the orphanage, they DO leave them with their mother and loving grandpa. Or else take them with them.
We aren't talking about ways of coping with a broken mechanism, we're addressing what's broken in it and proposing a fix. Why are you so defensive as to create consecutive so-so explanations/rationales to justify leaving the mechanic unchanged? It doesn't benefit you in any way, either way, so what's the deal?
For the record, I always allow them to join if they are bachelors. But married people with small children should not be asking to become celibate monks (exception: like 1 in 1000 with special permission from the Pope and consent from his wife to let him go and promise from his brother/uncle/friend/liege to take care of the kids, then only just maybe, even as per mediaeval Catholic theology). It's simply as anti-immersive as married chaplains.
Nonetheless, they shouldn't be asking if they are married, let alone consort of a ruler. As it stands all the holy order courts are full of people who shouldn't be there, and have no practical use.
Once upon a time, a lot of time ago, people, myself included, noted how then-orders were essentially social clubs of random-generated Levantine gentlemen. We suggested recruiting the dignitaries at least from existing noble families on the map. That was cool and dandy, except P-dox didn't restrict the manpool to bachelors (though married people with grown children were historically allowed to join monastic orders with their spouse's consent).
Maybe what's needed is to combine random generation with restricted recruitment of bachelors only.
In any case:
1. No married people*, but especially:
2. No people who have small children to care for. This was a biggie.
(* Spouse's consent to celibacy also worked, but it may be too much hassle to implement it to be worth it as opposed to the approximation in the form of banning all married people or all married people who have small children.)
***
Alternatively, there could be a way of joining the Templars and others that's open to married people —
but without removing them from succession. As was historically the case. Before they could become a high dignitary in the order, however (master, commander, councillor), they would need to become celibate. If they were
allowed to become celibate. Otherwise maybe lead armies like they were trained to do but no full membership and formal functions.
