Can I accept two offers from universities and decide later on
No.

In principle, you could do that, but it's not advisable, for the simple reason that if either school finds out you've accepted another offer, then both schools could end up rescinding their offers, and would be within their rights to do so. (Programs want to know how many spots they have filled, so that they can accept more people if needed to meet their enrollment targets.) 

Basically, you need to commit to one school only. If the offer is conditional, then you should weigh the probability of meeting those conditions before accepting the offer.