I help out at this chapel and we have a high altar and a novus ordo altar and since today is a Solemnity one of the head guys asks if we can light both the 6 high altar candles and the 6 novus ordo candles for the mass. Is this acceptable?
Where I have been…no, it would not be done nor allowed. The liturgical norms provide that on or near the altar of sacrifice there may be two, four or six candles. The gradation of number used being an indicator of the occasion being more or less solemn. A seventh candle may be lit, in essence the bugia, if a bishop is celebrating. Twelve candles for a Mass celebrated by a priest, even for a Solemnity, would be…exuberant.
(The calculation of candles used at Mass does not count candles such as the sanctuary lamp, which has a dedicated purpose, or again the Paschal candle or Advent wreath, or the devotional candles which the faithful may use; each of those are different from the distinctive candles properly and exclusively used for liturgical actions.)
The focus is rightly and properly oriented on the altar of sacrifice. If you have an altar or altars from another era that were deemed not removable, which can happen for a variety of reasons, they should be de-emphasised so all things rather point the focus of attention to the altar of sacrifice than toward these other items. Having the old high altar dressed with linens, decorated with candles (and and that equal in number to the altar of sacrifice) is working at cross purpose to that objective.
I would think that the parish priest would be obtaining direction on these matters from the diocese’s liturgical master of ceremonies and in consultation with the liturgy commission and the fine arts commission of the diocese (the latter assuming that the old high altar is there on grounds of artistic merit or antiquity), both to be established by the bishop – which will provide direction much sounder theologically and liturgically than seeking opinions on anonymous Internet fora.