multiple dynamics on a single note

You need to add second voice with (invisible) rests and add dynamics to them.

You may be lucky and find an easier way to do this when the future MS 4.1 is released. See the remark by @oktophonie:
https://musescore.org/en/node/346358#comment-1180287

At least in MuS 3.6.2 you also have to change the sound in the mixer from e.g. 'Trumpet' to 'Trumpet Expr.' and you need the right soundfont.

Or you can write out exactly what you want. What beat do you want the loudest? beat 2? Beat 4? For example write two half notes. Connect with a tie. Put a "P" on beat one, and an "F" on the second half note. Then a "P" on the first beat of the following measure. Put a crescendo hairpin on the first half note and a decrescendo hairpin on the second half note. This tell MuseScore and real players exactly what you want to happen. I know it doesn't look like what you might normally see.