I have a motorhome with a trimark handle model

Various help in the videos and the link. You need a shimming tool to spring the lock, or force it and fix any damage.

Not familiar with setup, but from what I can surmise there are at least two hydraulic cylinders that extend and retract the "room" and another, the "Synch", which makes sure the the two are at the same position

If opening is ok then system pressure may be low. Typical cylinders provide more force extending than retracting. Check pressure to spec.

If you have manual operation available, use it to check for any binding in mechanism. Determine cause and repair.

Whatever component you find is the problem, look into having it repaired/rebuilt/remanufactured. I've found cost to range from negligible to much less than 50% of new.

If your Class A has pass-through compartments, trying accessing from the opposite side and take some hand tools to unlock the latch or removing the striker for the latch. If, no pass-through, can you reach the locking mechanism from the compartment directly adjacent from either side. If so, try the same thing but reaching from the side. Another possibility is to use a wire, similar to a guitar string to feed under the latch to apply pressure to the inside of the slide bolt, what has the 45-60 degree angel to the strike plate. If you have to use this method, be patient and careful to avoid damaging the door seals.

Depending on the door latch configuration, you might be able to get a lubricant spray with a straw to spray in between the handle and the assembly to lubricate the internal pieces; if so, spray it and let it soak a while before trying to open the latch. Some of the new WD-40 penetrating sprays will tell you to let the liquid soak in to allow the best lubrication for the parts.

shore power or battery power, is your power in the back on? I have a switch just inside my side door to turn on power. Do you have to have your emergency brake on?

The weight is about 17000 lbs.

The weight is posted somewhere in the RV. Could be on a visor, inside a closet or cabinet door, or on a door panel.

it should be on the drivers door panel or inside on wall or under dash on drivers side

It may not be under the dash as in regular vehicles. They may be located under the hood or in a side compartment on the drivers side of the coach.

On the opposite side of the coach from the slide you need to manually close. You should see a hole through the frame. You should have also received a crank handle that has what seems to be a piece of pipe with a notch cut into it. Inside the referenced hole you should see a shaft with a roll pin through it. Insert the crank handle until it is seated on the shaft with the roll pin then begin to crank until the slide is retracted.

Why type of latch? Slam latch, small key cylinder, turn latch? Small key cylinders can be drilled out. The slam latches often can be manipulated by lifting the paddle handle and using a small screw driver activate the plunger. The turn handles are tougher and I would have to actually see to configuration to tell how to access it.

small screwdriver push in to latch pin if you can see it.