You'll need silver bearing solders, expensive.Or a similar alloy filler to weld it. But more importantly , skill is required. Without which your samovar will be ugly lumps of metal connected by slag holes.
Get some brass alloy and practice running different joints to perfection. The ability to play with liquidus/solidus in a small temperature range is the goal.
There is then the issue of expansion/contraction of the samovar and related stress questions that you will have to contend with. If it has profuse cracking it may well be beyond repair.

Brazing should do the trick.

It takes some practice, and an oxy-acetylene torch to do a good job.

Cadmium is the most common toxic element in brazing rods, but there are plenty of alloys that do not use cadmium.