DILEMMA Car seats!!!!!!!

So my daughter is 4 and in a catseat thats for big kids shell be in for a while.

The seat im buying for baby will be a 4in1 convert.

Both by Graco both pretty big

I have a 5 seater (sedan Lincoln MKZ).

Idk where to place the seats safely.

My 4yo is in the center for now.

Will they both have to go behind the driver and passenger? Should they sit next to each other one next to the window??

Where will I sit back there when baby arrives?

Im freaking bc T-bone and jack knife accidents are scary so Im crazy about proper installation.

Im a NYS resident so idk if that helps.

I just feel lkke my babies wont be safe....should I get a bigger car? Idk

Lastly, if Im being discharged for hospital will they not let me take baby bc I dont have an infant carrier but a convert w the infant feature installed?

My daughter had one and we spent alot of money upgrading so we learned our lesson then.

Plz dont be rude Im really dumbfounded and concerned. Just need advice.