No, it is not possible to convert them because FNT/PNG files are both raster and TTF/OTF files are both vector. Unless you want pixel versions of the fonts which you could recreate in something like FontStruct, no it is not possible to convert them. I don't know about the other fonts, but you can find Roobert here: Roobert - Displaay Type Foundry
EDIT: you can find it for free for personal use on other websites too