Arthur is rather disgruntled that he wasn't permitted to sit in on his underage son's interview but is allowed with his wife during hers. Not that he's ever disappointed to be by Molly's side but in this instance surely Ron needed him more.
When Molly is asked about Black she tries her hardest to come up with something useful, but it's obvious from the start that a thirty second look at a dog is not enough to base a criminal trial on. Arthur isn't surprised that Fudge is trying it anyway.
She ends up focussing more on Nymphadora's appearance during the visit than Black anyway. Arthur can't quite sympathise but he can admit that he'd been more wary of Andromeda than she'd ever given him reason too, based on looks and family alone. Of course, he'd felt quite sickly about himself when he realised.
No, Andromeda Tonks was a good women with bad relatives, and much as Arthur wanted to believe the easy version of the story – that Sirius Black was one of the bad ones and Andromeda was being sentimental and manipulated – he had to acknowledge that he'd never so much as met Black and had no way of having a proper opinion on the man outside of what the Prophet said. He knew better than to trust everything written in that rag.
But if Black wasn't guilty then that meant something awful about his boys' pet rat.
They hadn't been shown Pettigrew yet, but Charlie and Ron's word that it was real was enough for Arthur, who couldn't honestly say he wanted to have the truth of it shoved in his face at all.
As he sends them out after the questions, Albus asks them to wait a half-hour and then gather everyone and return. The minister adds that they don't need to fetch Black, which Arthur is glad for even though it seems to him that Black is the one who should be there the most.