Having your younger son drive you and then wait at the pub while you visit his brother’s house, is just plain weird. Is that what she expects? I’d ask her in a friendly fashion, “Is that what you mean?” And if she says yes, then just say “That would be weird. He (Son no 2) would have to come too”.
As an aside, we had to move into our house and live in one room and could use the kitchen and a shower and loo, whilst the builder was still here and had run over schedule. On about day 2 friends turned up unexpectedly to what was essentially a builder’s site, with flowers and a housewarming gift, and years later we still laugh with them about my expression when I opened the door, in shorts and a vest, streaked with dust and dirt and a headscarf! They were invited in and we had a cup of tea in the garden. Best to go with the flow!