I produce music and have done my share of covering songs originally performed by others. I've dealt with publishers representing The Beatles, ABBA, Eurithmics and many others, so I know a thing or two about music copyright.
As far as I know German music / copyright law allows anybody to make a cover version of existing music. This is actually what the OP is doing. When commercially exploited the credits for music and lyrics should be the same (unless agreed on differently e.g. because new lyrics are added) and normally the current IP holders (the music publisher) would get their money through sold MP3s / CDs, radio airplay and live performances where money is paid to organisations as ASCAP / BIEM and such.
Here an interesting part: The original record company, most likely the master owner of the original, makes no money on cover versions as it is not their master recording which is being commercialized.
E.g: Let's say Madonna recorded a song called "Holiday" in 1985. Her record company paid the studio in which she recorded the song and the producer of the song as well. That would make the record company owner of the master recording. Madonna may have written the music and the lyrics, but she may have signed with a publishing company not related to her record company. Let's call the publisher ABC and the record company XYZ. The record company makes money everytime THEY sell a recording of the song in a record store, i-tunes and such. They make no money on any copies sold second hand, but got paid the first time that music carrier was sold. Publisher ABC also gets a cut of new CD / i-tunes sales, as that is part of the copyright law. The publisher also makes money when the song is played on radio or tv.
Now if I would make a new recording of that "Holiday" song, which anybody is allowed to do as long as they credit the original composers, would recordcompany XYZ still make money on that? No, not unless they would have signed my recording and it would be commercialized by them. If I would sign with another recordcompany that company would be the one commercializing my version and making money on it. Record company XYZ may not like that, but it's not their master recording, so nothing they can do about it. The only exception could be if my recording would sample a part of the original recording by Madonna. In that case I would be using the original master recording, and then recordcompany XYZ can forbid me to exploit the recording. Or they can offer to make a deal so they can get a piece of the action.
Long story short: if the OP is making cover versions of the songs and voicecalls in WH2O they become his property. Williams would still be the publisher (although it remains to be seen whether they actually are) and Chris Granner still be the composer. Williams would not own the new master recording and as such is not entitled to any profits from commercialisation of it. If OP sells his new recordings commercially he should credit the original composers of music and lyrics and on regular sound carriers these composers would then get a royalty. This may be different when it comes to game ROMs as this is a less traditional type of sound carrier. The only thing unclear in this situation is whether PPS represents the original master owner and/or the publisher. Once that is clear you know what your position is.