I'd you want to push the issue you can report the abandoned camper van. It's only a matter of time before it's picked up on by the council and towed anyway, for having no tax.
He needs help to understand that what he's been offered is temporary accommodation.
And he's very very lucky to be offered anything other than a hostel or B&B where dogs aren't allowed. In my area there's only one offer of temporary accommodation made, turn it down and that's it - the council have no further duty to help you.
He can accept the temporary accommodation and still come sit in the camper van all day during the day/evening, eat there etc if he wants (until it's towed away). He doesn't have to stay cooped up in the temporary place for the duration of his stay. It's just somewhere to put his few possessions/food, sleep and get washed/toilet.
Charity, Freecycle or council grant will help him get furniture, which he can take to new place when he leaves or dispose of as he wishes.
He needs to understand that classed as homeless he'll get a permanent property sooner and he'll have choice in where that property is and what sort of property.
He could choose sheltered housing or ordinary housing. Ground floor with a garden or higher up if he prefers that, maybe with a small balcony. Property in a block with communal facilities like an extra lounge (as well as the personal lounge in his property). Or house converted into flats each with their own entrance. Or bungalow. Whatever is available. There's time for him to think about and choose what to 'bid' on each week (which means registering his interest in a property).
If he turns down the temporary accommodation he won't be classed as homeless and it will be years until he's offered a permanent property from the bidding list as he'll be classed as low priority.
He will be evicted from the camper van long before he gets a permanent property.
He needs to accept the temporary accommodation now because it's a choice between, in a few weeks, either that or living rough on the streets.
He's 72 the permanent property he's likely to get could be a really nice place in sheltered housing. With reasonable neighbors hopefully. A ground floor flat or bungalow with a bit of a garden for the dogs. But the way to get that, or whatever property he'd prefer, is to accept the temporary accommodation.
If he ends up living rough, he'll end up sick, he'll be hospitalised and they will end up putting him in an old people's home due to not being able to look after himself. Because choosing to live on the streets as a vulnerable, frail (he will be frail half starving on the streets, if he isn't already), elderly person isn't looking after yourself. The choice will be taken away from him, he'll be deemed to lack capacity to make his own welfare decisions. If that happens, it's bye bye dogs.
Can someone look after the dogs while someone else gets him to his GP (phone the GP first, so they're aware of the situation. They won't be able to discuss him because of confidentiality, but they can listen to what you say and book an emergency appointment for him). Old people often respect the opinion of people like doctors more, so if the doc tells him to take the temporary accommodation and spells out the consequences if he doesn't, it might work.