The poll wasn't asking if they wanted him to be POTUS or be in anyway involved in US politics - it was just to find a person both Rs & Ds looked on favourably. That's great news for Britain when it comes to influence & aoft diplomacy.
And he is happily married, has good, friendly relationships with his wife's family, his father & his aunts & uncles & his cousins.
I don't think the fact he currently has a strained relationship with his brother & sister-in-law (who are also estranged from her family) really indicates much tbh.
Overall, his family relationships seem pretty happy and strong. Lots of people have 1 relation they don't get on with.