My xH and I have been apart for over 10 years. He married his OW and they have a DS aged 6-7ish.
My DSs used to see their dad every other weekend. Eldest at Uni and rarely sees his dad even when he's home from Uni. Youngest still does the alternative weekend thing although it at Sixth Form but feels he's often a babysitter at his dad's (and only gets £5 for a night's sitting his half-brother).
Both DSs have said they feel their dad prefers his youngest son (their half-brother), and that they really don't care that much for them, and that he takes very little interest in their lives.
I have asked him in the past to take more notice of their feelings but was told I was I was stirring things up.
AIBU to want to try again in the hope he can demonstrate to them they he loves them and is interested in them, and that his new son isn't his favourite.