Struggling with DS's routine

[SighingMum23]

I am trying to shake DS off from his nap as he is not napping til 4/5 and that is far too late pushing his bed time to 11.

Whenever I get on a no nap routine, DH completely ruins it or it is ruined by expectations from family. I want DS to have an 8-8 routine. DH will put him to sleep when he pleases and expect me to pay the price of it by waking at ridiculously early times or sleeping at ridiculously late times.

I also have a small baby so I really don't want this extra hassle.

How would you approach this? I have given DH one last chance otherwise I am taking over as it's really causing me to go insane.

How old is DS?
Can you just cut him down to 45 mins or so if he really does still need one

He is 2.5 years old, his nap is about that long when he does have one. He has been on an 8-8ish routine for about 2 weeks and it worked well. On long journeys he does knock off though.