Hello,

Yes 10th and 12th marks matter in campus placements. They are used for eligiblity purpose. Many companies now a days only allow students who have more than 60-65%(depends on company) to sit in placements. 

With this marks you have less chances of campus placements. But you can apply for off-campus placements as many companies does not take into into consideration 10th marks. 

Yes you can It all depends upon the company's basic eligibility criteria.

After MTech, most of the companies focus on your dissertation/project worm rather than looking at the previous percentage, but in case if they question your less percentage in XII, you've to answer them accordingly. Just build yourself for the interview round to answer each and every question that'll help you.

Feel free to comment if you have any doubt
Good luck