DIY Mulling 10 foot X 4 foot window

Hi. I have an existing vinyl picture window with 2 double hung flankers that I want to replace (the glass seals have failed). If possible, I would like to do myself. The picture windows is 48H X 55W. The double hung flankers are 48H X 32W.

So, the total window assembly is just about 10 feet long by 4 feet high. If it is factory mulled, I think it would be impossible for me to install this by myself. I would probably need 4 strong guys, which I don't have.

1. Are some window brands easier to field mull than others? I am going to go with vinyl or fiberglass.

2. Is it possible to put one unit into the rough opening at a time (loosely secure it), and then mull the units together in the rough opening?

3. Or could I build a temporary platform in front of the rough opening. Assemble the windows together on the platform and then slide the assembly in.

4. Or should I just get these professionally installed?

Most of the newer mulls can be field mulled and are somewhat easy to work with in that scenario.

The clip in field mulls are much more secure these days.

You can either field mull on the ground or in the opening if the windows use a c mull.
You can order the unit factory mulled(best choice), take the sash out of the flankers( two guys max), lift unit into opening, pin in opening, reinsert sash, finish install.