Tips To Playing Challenging Rhythms And Singing/backing Up

As the title implies, is there anyone with a good tip or advice on the subject?
I used to be utterly crap at singing and playing at the same time, but just trying over and over helped me out a lot. My challenge now is if I`m not even able to sing for one second without losing the rhythm, even though the rhythm is really simple to play, I don`t know how to practice it

For reference, the song I`m trying to play and support backing vocals to is Kool and the Gang - Celebration, while playing bass
...I also struggle a lot more when playing bass then guitar. As if I feel more of a responsibility for being tight. Does anyone feel the same?

Blues Soloing - Beginner/Intermediate

Original lesson: Blues Soloing - Beginner/Intermediate by Ivan Milenkovic

Basic Rock Guitar: Advanced Power Chords

Original lesson: Basic Rock Guitar: Advanced Power Chords by Guido Bungenstock

Awesome lessons and great practise in muting chords with a lot of gain. I`d also love feedback on tone and what can be done EQ-wise. Wanting to get a bit more in to that area (Seems like the video clips a lot on youtube - not sure if that is due to new camera/phone or just that it is not finished processing. Let me know)

Stoner for Strat (rhythm & solo)

Original lesson: Stoner for Strat (rhythm & solo) by Darius Wave

Perfect lesson to get started with REC again after some lazy summer weeks :D After finishing the video, I realize I should have spent a bit more time tweaking the tone to get a more bottly sound, but I was too eager to get this one out htere!

Chord Melody Technique

Original lesson: Chord Melody Technique by Diego Budicin

To me, this was way above a level 3. But then again, probably just a sign I need to work on it.