The tables of the database of my application, for registration of
user, etc., can be made in MYSQL and hosted on a server and
access this data by the application?
Yes, they can do it in Mysql. In fact the database used for data storage and access on the server side is indifferent; and the decision of choice between a "brand" and another varies according to the need of the project.
That way, I need to use Sqlite as well?
It depends. If you think about developing some mechanism to cache the captured data from the server, Sqlite can be very useful.
How different users can keep information up to date?
This question is hardly difficult to answer because it is a bit wide. It depends on your business rules. If your system was a voting system, for example, users would keep their data up to date as they cast their vote. Then you could get real-time information about who was winning the vote.
Yes, no problem. Only one database can be used on the server side, one client side bank, or both together.
– Giancarlo Abel Giulian