Regarding the Belauan government surrendering quickly and the comparison to Hawaii, well the reason Queen Lili'uokalani didn't fight back is a lot more complicated than her just "giving up". Her hope was that by going through diplomatic channels, the US would realize that what happened was illegal and support the restoration of the monarchy. She actually had a reason to believe this would happen, as years previously the United Kingdom had invaded and occupied Hawaii over some land disputes involving British citizens and raised the British flag over Hawaii, directly taking over the government. The occupation was ended after diplomatic protestations directly to London from King Kamehameha III (see the Paulet Affair for more details).
Belau doesn't have this precedent, so they probably wouldn't give up so easily. I'm just not sure how keen the King would be to fight a war when he knows that his military on it's own wouldn't be able to do anything and that he'd need to wait for foreign intervention to even stand a chance. He'd probably de facto not fight to avoid unnecessary deaths, but not surrender de jure and instead ask for foreign intervention to try and prevent it.
But regarding Lanlania's stuff:
Belau doesn't have this precedent, so they probably wouldn't give up so easily. I'm just not sure how keen the King would be to fight a war when he knows that his military on it's own wouldn't be able to do anything and that he'd need to wait for foreign intervention to even stand a chance. He'd probably de facto not fight to avoid unnecessary deaths, but not surrender de jure and instead ask for foreign intervention to try and prevent it.
But regarding Lanlania's stuff:
- Guaranteeing Sentric religious freedom in Belau - okay, acceptable.
- Accepting Sentric missionaries in Akitsu - could be acceptable, though again the government would probably quickly make a law allowing for freedom of religion and allowing other missionaries. Also don't expect to displace Reido as the dominant religion of Akitsu.
- Support HLE in southern Ostara - if it's a mutual alliance, than sure! Akitsu would be worried about Oslanburg since Oslan would have expanded pretty close to Akitsu's borders when the took Singan. If it's a mutual thing, Akitsu would likely see it as a win-win.
- Maybe through Royal Marriage? - maaaaaaybe, but don't expect to have an heir to Akitsu's throne born from this