PB put only two return lines (plus one for cleaner). Both return lines run from one 2" supply. Based on calculations 2" can supply 76GPM and 35000G pool will need 73GPM for 8h turn over.
Does that look like a problem running on maximum pipe capacity? Will it cause pump to not run efficently?
Should we put separate 2" pipe for each return? Add another turn?

Two skimmers have separate 2" lines to the pump. No main dains.

I would use a separate 2-inch PVC pipe for each return.

How far will the equipment be from the pool?

Commercial pools really need three or four turnovers a day, but a residential pool is totally fine with two turnovers a day, or even less. "Maximum" flow rates for PVC pipe are not hard limits, you can always pump more water through the pipe it just gets progressively less efficient.

For a pool that size it is certainly a very good idea to run at least two 2" pipes in each direction, preferably three, but everything will still work even if you only have one pipe each direction.

I am a newbie in the middle of a DIY 20 x 40 vinyl install, so I am not an expert. But I would be concerned. Returns are not that expensive considering what they give you. I have 3 returns in the walls 2 on one line 1 on it own, 2 in the steps on their own line, plus I have 4 deck jets and a slide that will help circulate water each on their own line. I also do not have a main drain, two of my returns will be aimed at the bottom of the pool. All is 2".

PB builder put another return line. So I have now two lines from skimmers, and two lines for three returns.
Looks like I am ok now.
Thank you guys for responding.