Halito, I personally would not keep 2 Oscars & 2 Jacks in a 75 G. They need growing space.
I have one JD and one orange Tiger Oscar in a 110. They came to me from a previous owner. She had them together for about 5 years in an overcrowded 125 G. More tacky decor than water. Several huge blood red parrots and a big pleco in addition to Jack and Oscar (yes, those are my clever names for this pair.) Oscar is only 8” long and it’s possible the crowded conditions stunted his growth. idk The JD is a bottom dweller & relatively inactive, but oh! So beautiful with his turquoise polka dots.
I have another Oscar, 8” long, also from an overcrowded tank, a 90 G. Again giant flying saucers next to Greek ruins and humongous plastic plants. All kinds of other fish. This Oscar is said to be 8 yrs old. She’s in a 125 G with six Clown Loaches: 4 are ~4”, one is 5 and the largest ~6. Future plans are to get a bigger tank.
These fish and the tanks and some very nice canister filters etc etc were found in local FB groups. FB was never my thing until the owner at Imperial Tropicals suggested I join his group. That led
to local groups & all kinds of bargains & specialty groups for individual species I keep. In case you’re unfamiliar, Imperial Tropicals in Florida is my all time favorite online fish seller. They have species impossible to find locally. However, I’m doing very well getting some wonderful fish from private parties that are far less costly, if not free, & don’t involve the $40 overnight shipping fee. But I continue to buy from Imperial.
BTW, your fish are beautiful!