I don't fully follow that but like I said, sounds like you're doing it wrong if you have to alter firewall rules every time you add a host because of DNS issues.
I use Seafile for this. Switched after getting fed up of fixing Nextcloud every time I updated it.
What are you expecting them to do with your IP?
No idea. Depends how much it costs you to host your own server?
Does hosting it yourself cost more or less than €12 per 30 days?
Simplest option: Switch to Gmail and add your domain as an alias.
Not so simple, but not by a great deal: Switch to Zoho.
They won't just plug in to your network and share access with anyone as some other commenter is suggesting. They want to protect their customers from you as much as you want to be protected from them.
You really need to ask them, we don't know what they are fitting or how they are doing it. Surprised they are sharing your internet, I started a WISP and when we did this we'd have our own connection, we wouldn't just share the homeowners internet.
DokuWiki. Quite a few natty plugins to go with it, light, simple, host anywhere.
Love seeing a rack mounted next to a sewage access plug!
Yeah the IP:s are there for the world to see, but you won't easily know they belong to me unless I point to them from my domain.
As has been pointed out though, it makes no difference and no-one cares. No-one is manually cross referencing IP's and domains, and besides, what difference will it make anyway?
I've heard this argument before with someone saying they use DDNS on all customer sites instead of static IPs as it's "more secure" because there's a website out there with exposed desktops listed on it.
Buy a cheap NVR. Much easier than pissing about with servers and Windows. Most will have a partner app and simple cloud connectivity. Much easier all round.
Pretty much anything could do this, can even do it with an Excel document!