Shardul, T. Natarajan, and Kartik are already there as net bowlers. Even though I am very excited about Kartik and his potential, he is still very raw, and it's definitely not a good idea to add him to the test squad right now. So, I am pretty sure it will be Shardul and Natarajan who will be added as replacements for Umesh and Shami.
Shardul Thakur is obviously more experienced than Natarajan when it comes to first-class cricket, and his batting is only going to help his case. The only thing in favour of Natarajan is the variety he will provide with his left arm.
However, Saini was already in the squad, so it will be interesting to see who will replace Umesh in the final 11. I know Saini is regarded as a better red ball bowler than a white-ball bowler, but his discipline will be something that will be important.
It is crazy to think that we don't have Ishant, Shami, Umesh and Bhuvi, and we are still 1-1 in this test series. It is ridiculous how injury-prone Bhuvi has become in the last few years. I was also hoping to see Ishant at some point in this tour, but it is unfortunate that he needs to prove his match fitness before playing.