1

Madagascar is completely different from the Seychelles (where I once lived) and Mauritius. The journey time-consuming and expensive, so I suggest you simply spend more time on Madagascar.

It has often been said that while Mauritius has coral reefs and beaches, and Reunion has mountains, the Seychelles has got the lot. The sheer natural beauty of the Seychelles is breath-taking in a way that is not at all the case with Mauritius. Having said that, I got bored with the Seychelles fairly quickly and I think Mauritius would be more fulfilling for a longer 'cultural' and active holiday.

The Seychelles would be a good place to relax after an active visit to Madagascar, but you could achieve the same objective by visiting Nossi Be.

2

how do we come from Madagascar to the Seychelles?

You could make that route with Kenya Airways changing planes in Nairobi or with Air Austral changing planes in Reunion (St. Denis). In both cases, you could need to stay overnight in the city where you change planes and, perhaps, to purchase two separate tickets (one for each leg). Take a look at the webs of both airlines to look for schedules and fares.
Another option is to fly from Madagascar to Mauritius with any of the airlines flying between both countries and take another flight from Mauritius to Mahé (take a look at the web of Air Seychelles for info about the leg from Mauritius to Mahé).