Depending on what camping conversion the interior you might get them inside but I think it’ll be tight especially if you have much kit etc.
Mine is a devon and you can just about get a hardatil in between the benches or a DH bike with a wheel off but either is awkward.
Additionally if your bikes are muddy then you’ll get mud over where you will be sleeping.
Realistically its not practical.
I can say 100% without complete disassembly you will not get two people and two bikes in over night…
To be honest a camper is a lot smaller inside than you realise and is really only suited to one person or a small couple.
The best bet is a T2 type Fiamma bike rack specifically for the T2 van.
Security wise well you could pop a look off a T2 van by locking at it hard. And I’d be checking that what ever you lock your bike to is held on by more than a veneer of rust…