Are these sentences correct?

Hello, everybody.

I am 90% sure the following sentences are incrorrect, but I need 100%:

Ex1.: He doubts if they visit their uncle tomorrow.
Ex2.: He doubted if they visited their uncle the next day.

Thanks in advance.

They are both incorrect. They should be:

1 - He doubts that they'll visit their uncle tomorrow.
2 - He doubted if they had visited their uncle the next day.

Thank you very much, american nic.

If we were expressing a doubt preceding to the visit the second would be:
2. He doubted if they would visit their uncle the next day.
Your variant is for the case 'doubted' happend after 'visited'.

Am I right?

Your second sentence was almost right Ant_222.
This is what I would have said:

" He doubted that they would visit their uncle the next day".

Yes, sorry for the confusion. For mine, he's doubting after the alleged visit.

Thank you. You helped a lot.