7 x 20 = 140 you have 105 simple maths no you can't power them from the same transformer. 105 / 7 = 15 normally rated 35 ~ 105 so 35 / 7 = 5 so if you used LED lamps between 5 and 15 watt it should work as long as they are designed for that transformer, many G5.3 lamps are marked 50 Hz and many electronic transformers give out power in the MHz range so they may not work.
In the main people today shy away from extra low voltage because of compatibility issues, today most use low voltage with GU10 bases.
Note MR16 is multifaceted reflector 16/8th inch across does not matter which base. Extra low voltage under 50 volt ac. Low voltage 50 to 1000 volt ac.
105VA is equivalent to the maximum demand/load in watts the transformer can deal with. But it would be foolish to have the transformer working at maximum output, I would recommend that you leave at least 15% unused.
Watts = Volts x Amps x Power factor correction, in the main the power factor is around unity so VA and Watts means nearly the same, I do think it is poor how the transformer is rated in VA and the lamp in Watts, but the EU rules say the bulb has to be labelled in watts, and to ensure a transformer is not overloaded it has to be labelled in VA. So typical electronic transformer is 105 VA and two G5.3 bulbs are likely 50W each so there is 5 VA to spare in case PF is not unity.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!