Do I need to replace these metal support posts

How tall are your posts to start with? A 6 foot above ground post should have at least 2 feet in the ground in your area. I would be setting them in concrete so you have a good solid base and good ballast. A metal post in concrete won't rust as long as you dome the top of the concrete so water runs away from the post.

I'll share a clever trick that works well and is very fast. After digging your hole for the post, set one or two bricks in the bottom of the hole to set your post on. You will of course have to adjust for height and plumb the post. Then simply pour an 80 pound bag of Sacrete premixed concrete mix around the post dry, right from the bag. Now just pour apx 2 gallons of water on top of the mix and leave it alone for 24 hours. You will have a solid concrete base for your posts without having to mix concrete. Mixing concrete is good, even better, but this little trick is fast and easy.

The vertical posts are probably almost strong enough for only two supports as is. Replacing those with steel is not necessarily needed.

The challenge is the strength of the horizontal span with reduced supports. If left as wood, it will have to be fortified by a factor of more than two. Of course, the added weight of that much more beam means the factor must be increased a little more.

Assuming #1 northern Doug-fir for a span holding roofing only which is 20 lbs/sq ft live load plus 10 lbs/sq ft dead load and assuming that the current spans were engineered at 150%, then increasing the current 10-11 ft spans to 30 feet would require replacing the pair of 2x6s with a pair of 2x12s on edge, firmly tied together.

I tried to figure out an equivalent steel beam, but I am out of my experience. The first result says that a 4x4.5 inch beam is more than twice what is needed. Searching for rough pricing for such beams is surprisingly challenging.