Translation:Kateřina married their youngest son.
No, it is not. Took sounds like Katerina is a kidnapper. To suggest the same thing in Czech you would have to skip the SI part. Kateřina vzala jejich nejmladšího syna. But when speaking about people and VZIT is relexive in that sentence it means to marry.
Oni se vzali. = they took each other = they got married
Oni vzali = they took.. it is missing in both languages what it is they took.
when you talk about something else than people, VZIT SI is to HAVE A PIECE OF SOMETHING. As in to help yourself to food. If you are offering food to people you encourage them with "VEZMI/VEZMĚTE SI'